Metal powder for powder metallurgy, compound, granulated powder, sintered body, and method for producing sintered body

ABSTRACT

A metal powder for powder metallurgy includes particles each having a first region containing Fe as a principal component, a second region, in which the content of a first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and a third region, in which the content of a second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region. Further, the first region occupies 50% by volume or more of each of the particles and also is crystalline.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2014-063428 filed on Mar. 26, 2014 and Japanese Patent Application No. 2015-005131 filed on Jan. 14, 2015. The entire disclosures of Japanese Patent Application Nos. 2014-063428 and 2015-005131 are hereby incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a metal powder for powder metallurgy, a compound, a granulated powder, a sintered body, and a method for producing a sintered body.

2. Related Art

In a powder metallurgy method, a composition containing a metal powder and a binder is molded into a desired shape to obtain a molded body, and the obtained molded body is degreased and sintered, whereby a sintered body is produced. In such a process for producing a sintered body, an atomic diffusion phenomenon occurs among particles of the metal powder, and thereby the molded body is gradually densified, resulting in sintering.

For example, JP-A-2012-87416 proposes a metal powder for powder metallurgy, which contains Zr and Si, and in which the remainder contains at least one element selected from the group consisting of Fe, Co and Ni, and inevitable elements. According to such a metal powder for powder metallurgy, the sinterability is enhanced by the action of Zr, and a sintered body having a high density can be easily produced.

The thus obtained sintered body has become widely used recently for a variety of machine parts, structural parts, and the like.

However, depending on the use of the sintered body, further densification is needed in some cases. In such a case, a sintered body is further subjected to an additional treatment such as a hot isostatic pressing treatment (HIP treatment) to increase the density, however, the workload is significantly increased, and also an increase in the cost cannot be avoided.

Therefore, an expectation for realization of a metal powder capable of producing a sintered body having a high density without performing an additional treatment or the like has increased.

SUMMARY

An advantage of some aspects of the invention is to provide a metal powder for powder metallurgy, a compound, and a granulated powder, each of which is capable of producing a sintered body having a high density, a sintered body having a high density, and a method for producing a sintered body capable of producing a sintered body having a high density.

The above advantage is achieved by the configurations described below.

A metal powder for powder metallurgy according to an aspect of the invention is a metal power in which when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the metal powder includes particles each having: a first region containing Fe as a principal component; a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region; and a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and the first region occupies 50% by volume or more of each of the particles and also is crystalline.

According to this configuration, when the metal powder for powder metallurgy is subjected to powder metallurgy, the second region and the third region move to a metal crystal grain boundary in a sintered body, so that the significant growth of crystal grains is prevented, and thus, a sintered body having finer crystals can be obtained. As a result, a sintered body having a high density can be obtained without performing an additional treatment.

In metal powder for powder metallurgy according to the aspect of the invention, it is preferable that the content of O in each of the second region and the third region is higher than in the first region.

According to this configuration, in the particles, Fe and the like are easily reduced, and therefore, the amount of oxygen contained inside the crystal becomes relatively smaller. Due to this, the sinterability of the metal powder for powder metallurgy is further enhanced, and thus, a sintered body having a higher density can be obtained.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferable that the second region and the third region are present in the first region and are disposed apart from each other.

According to this configuration, the structural uniformity of the particles is further enhanced, and therefore, an effect of fining crystal grains in a sintered body can be uniformly exhibited. As a result, a more homogeneous sintered body can be obtained.

In the metal powder for powder metallurgy according to the first of the invention, it is preferable that in the cross section of each of the particles, the second region and the third region each have a particle form, and the particle diameter of each of the second region and the third region is 0.01% or more and 0.9% or less of the particle diameter of the particle.

According to this configuration, the second region and the third region more easily move to a metal crystal grain boundary in a sintered body, and therefore, the significant growth of crystal grains can be more reliably prevented. As a result, a sintered body having a higher density and high mechanical properties can be obtained.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferable that in each of the particles, the first region is formed from a single crystal.

According to this configuration, when the metal powder for powder metallurgy is subjected to powder metallurgy, the second region and the third region are considered to more easily move to a metal crystal grain boundary in a sintered body. As a result, the increase in the size of crystals is more reliably prevented, and thus, a sintered body having finer crystals can be obtained.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferable that in the metal powder for powder metallurgy, the particles are contained in an amount of 50% by number or more.

According to this configuration, an effect of fining crystal grains brought about by the second region and the third region becomes more prominent, and thus, a sintered body having fine crystals can be more reliably produced.

In the metal powder for powder metallurgy according to the aspect of the invention, it is preferable that each of the particles contains: Fe as a principal component; Cr in a proportion of 10% by mass or more and 30% by mass or less; Si in a proportion of 0.3% by mass or more and 1.2% by mass or less; C in a proportion of 0.005% by mass or more and 1.2% by mass or less; the first element in a proportion of 0.01% by mass or more and 0.5% by mass or less; and the second element in a proportion of 0.01% by mass or more and 0.5% by mass or less.

According to this configuration, a metal powder for powder metallurgy capable of producing a sintered body having a high density, and also high corrosion resistance and high mechanical properties can be obtained.

A compound according to another aspect of the invention contains the metal powder for powder metallurgy according to the aspect of the invention and a binder which binds the particles of the metal powder for powder metallurgy to one another.

According to this configuration, a compound capable of producing a sintered body having a high density can be obtained.

A granulated powder according to still another aspect of the invention is obtained by granulating the metal powder for powder metallurgy according to the aspect of the invention.

According to this configuration, a granulated powder capable of producing a sintered body having a high density can be obtained.

A sintered body according to yet another aspect of the invention is a sintered body in which when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the sintered body includes: a first region containing Fe as a principal component; a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region; and a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region.

According to this configuration, a sintered body having a high density can be obtained without performing an additional treatment.

In the sintered body according to the aspect of the invention, it is preferable that the content of O in each of the second region and the third region is higher than in the first region.

According to this configuration, a sintered body having excellent mechanical properties can be obtained.

In the sintered body according to the aspect of the invention, it is preferable that in the cross section of the sintered body, the second region and the third region each have a particle form with a particle diameter of 10 nm or more and 1000 nm or less.

According to this configuration, the second region and the third region contribute to the prevention of oxidation of Fe or the like without deteriorating the mechanical properties of the sintered body, respectively, and therefore, a sintered body having particularly excellent mechanical properties can be realized.

A method for producing a sintered body according to still yet another aspect of the invention includes: molding a composition containing a metal powder for powder metallurgy, thereby obtaining a molded body; and firing the molded body, thereby obtaining a sintered body, wherein when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the metal powder for powder metallurgy includes particles each having a first region containing Fe as a principal component, a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and the first region occupies 50% by volume or more of each of the particles and also is crystalline.

According to this configuration, a sintered body having a high density can be obtained without performing an additional treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a view schematically showing a cross section of particles included in an embodiment of a metal powder for powder metallurgy according to the invention.

FIG. 2 is a partial enlarged view (an enlarged view of a region surrounded by an alternate long and short dash line) of a cross section of the particle shown in FIG. 1.

FIGS. 3A and 3B show an example of a transmission electron microscope (TEM) image of a cross section of a particle contained in a metal powder for powder metallurgy according to the invention.

FIG. 4 shows an example of the results of a mapping analysis by energy dispersive X-ray spectrometry of the cross section of the particle shown in FIG. 3B.

FIGS. 5A and 5B show an example of a TEM image of a cross section of a particle contained in a metal powder for powder metallurgy according to the invention.

FIGS. 6A and 6B show an example of a TEM image of a cross section of a particle contained in a metal powder for powder metallurgy in the related art.

FIG. 7 is a view schematically showing a cross section of an embodiment of a sintered body according to the invention.

FIGS. 8A and 8B show an example of a transmission electron microscope image of a cross section of a sintered body according to the invention.

FIG. 9 shows an example of the results of a mapping analysis by energy dispersive X-ray spectrometry of the cross section of the sintered body shown in FIG. 8B.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a metal powder for powder metallurgy, a compound, a granulated powder, a sintered body, and a method for producing a sintered body according to the invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

Metal Powder for Powder Metallurgy

First, an embodiment of a metal powder for powder metallurgy according to the invention will be described.

In powder metallurgy, a sintered body having a desired shape can be obtained by molding a composition containing a metal powder for powder metallurgy and a binder into a desired shape, followed by degreasing and firing. According to such a powder metallurgy technique, an advantage that a sintered body with a complicated and fine shape can be produced in a near-net shape (a shape close to a final shape) as compared with the other metallurgy techniques is obtained.

With respect to the metal powder for powder metallurgy to be used in the powder metallurgy, an attempt to increase the density of a sintered body to be produced by appropriately changing the composition thereof has been made. However, in the sintered body, pores are liable to be generated, and therefore, in order to obtain mechanical properties comparable to those of ingot materials, it was necessary to further increase the density of the sintered body.

For example, in the past, the obtained sintered body was further subjected to an additional treatment such as a hot isostatic pressing treatment (HIP treatment) to increase the density. However, such an additional treatment requires much time, labor and cost, and therefore becomes an obstacle to the expansion of the application of the sintered body.

In consideration of the above-described problems, the present inventors have made extensive studies to find conditions for obtaining a sintered body having a high density without performing an additional treatment. As a result, they found that the density of a sintered body can be increased by optimizing the structure of each particle contained in a metal powder, and thus completed the invention.

Specifically, the metal powder for powder metallurgy according to this embodiment includes particles, which are configured such that a first region P1 containing Fe as a principal component, a second region P2 mainly containing a first element described below and Si, and a third region P3 mainly containing a second element described below and Si are formed in the same particle. Further, the first region P1 occupies 50% by volume or more of each of the particles and also is crystalline. By using the metal powder containing such particles, when the particles are sintered in a firing step, the sintering is promoted and the density is increased. As a result, a sintered body having a sufficiently high density can be produced without performing an additional treatment.

Further, such a sintered body has excellent mechanical properties, and therefore can be widely applied also to, for example, machine parts, structural parts, and the like, to which an external force is applied.

The first element is an element selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta, and the second element is an element selected from the group consisting of the above-described seven elements, and having a larger group number in the periodic table than that of the first element or an element selected from the group consisting of the above-described seven elements, and having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element.

Hereinafter, the configuration of the metal powder for powder metallurgy according to this embodiment will be described in further detail. In the following description, the metal powder for powder metallurgy is sometimes simply referred to as “metal powder”, and the particles forming the metal powder for powder metallurgy are sometimes simply referred to as “particle”.

FIG. 1 is a view schematically showing a cross section of particles included in an embodiment of the metal powder for powder metallurgy according to the invention, and FIG. 2 is a partial enlarged view (an enlarged view of a region surrounded by an alternate long and short dash line) of a cross section of the particle shown in FIG. 1.

The particle 1 shown in FIG. 1 is formed from an Fe-based alloy and contains the first region P1, the second region P2, and the third region P3 as shown in FIG. 2. Among these regions, the first region P1 shown in FIG. 2 occupies 50% by volume or more of the particle 1. This volume ratio can be simply obtained from the ratio of the area occupied by the first region P1 in the cross section of the particle 1. On the other hand, the second region P2 and the third region P3 shown in FIG. 2 each have a particle form and are scattered apart from each other in the first region P1.

The first region P1 is a region containing Fe as a principal component. Such a first region P1 can be dominantly present also after sintering the metal powder, and therefore has an influence on the mechanical properties of the sintered body. By setting the first region P1 to be a region containing Fe as a principal component, the sintered body has excellent mechanical properties derived from an Fe-based alloy.

The first region P1 is only required to have an Fe content of 50% by mass or more.

On the other hand, in the second region P2, the content of the first element is higher than in the first region P1, the content of Si is higher than in the first region P1, and the content of Fe is lower than in the first region P1.

In other words, when the content of the first element in the first region P1 is represented by E1 (P1), the content of the first element in the second region P2 is represented by E1 (P2), the content of Si in the first region P1 is represented by Si (P1), the content of Si in the second region P2 is represented by Si (P2), the content of Fe in the first region P1 is represented by Fe (P1), and the content of Fe in the second region P2 is represented by Fe (P2), the first region P1 and the second region P2 in the particle 1 satisfy all the relations represented by the following formulae (1) to (3).

E1(P2)>E1(P1)  (1)

Si(P2)>Si(P1)  (2)

Fe(P2)<Fe(P1)  (3)

Further, in the third region P3, the content of the second element is higher than in the first region P1, the content of Si is higher than in the first region P1, and the content of Fe is lower than in the first region P1.

In other words, when the content of the second element in the first region P1 is represented by E2(P1), the content of the second element in the third region P3 is represented by E2(P3), the content of Si in the third region P3 is represented by Si(P3), and the content of Fe in the third region P3 is represented by Fe(P3), the first region P1 and the third region P3 in the particle 1 satisfy all the relations represented by the following formulae (4) to (6).

E2(P3)>E2(P1)  (4)

Si(P3)>Si(P1)  (5)

Fe(P3)<Fe(P1)  (6)

When the particles 1 including such a first region P1, a second region P2, and a third region P3 are subjected to powder metallurgy, the densification during sintering is particularly enhanced. As a result, a sintered body having a high density can be produced without performing an additional treatment.

By densifying a sintered body, a sintered body having excellent mechanical properties can be obtained. Such a sintered body can be widely applied also to, for example, machine parts, structural parts, and the like, to which an external force is applied.

Hereinafter, one example of the composition of the Fe-based alloy forming the particle 1 will be described in further detail.

Fe is a component (principal component) whose content is the highest in the Fe-based alloy and has a great influence on the properties of the sintered body. The content of Fe in the whole particles 1 is 50% by mass or more. According to this, in the first region P1 which occupies 50% by volume or more of the particles 1, Fe is contained as a principal component.

Si

Si (silicon) is an element which provides corrosion resistance and high mechanical properties to a sintered body to be produced, and by using the metal powder containing Si, a sintered body capable of maintaining high mechanical properties over a long period of time can be obtained.

The content of Si in the metal powder is set to preferably 0.3% by mass or more and 1.2% by mass or less, more preferably 0.4% by mass or more and 1% by mass or less, further more preferably 0.5% by mass or more and 0.9% by mass or less. If the content of Si is less than the above lower limit, the effect of the addition of Si is weakened depending on the overall composition so that the corrosion resistance and the mechanical properties of a sintered body to be produced may be deteriorated. On the other hand, if the content of Si exceeds the above upper limit, the amount of Si is too much depending on the overall composition so that the corrosion resistance and the mechanical properties may be deteriorated instead.

First Element and Second Element

The first element and the second element deposit a carbide or an oxide (hereinafter also collectively referred to as “carbide or the like”). It is considered that this deposited carbide or the like inhibits the significant growth of crystal grains when the metal powder is sintered. As a result, as described above, it becomes difficult to generate pores in a sintered body, and also the increase in the size of crystal grains is prevented, and thus, a sintered body having a high density and excellent mechanical properties can be obtained.

In addition, although a detailed description will be given later, the deposited carbide or the like promotes the accumulation of silicon oxide at a crystal grain boundary, and as a result, the sintering is promoted and the density is increased while preventing the increase in the size of crystal grains.

The first element and the second element are two elements selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta, but preferably include an element belonging to group 3A or group 4A in the long periodic table (Ti, Y, Zr, or Hf). By including an element belonging to group 3A or group 4A as at least one of the first element and the second element, oxygen contained as an oxide in the metal powder is removed and the sinterability of the metal powder can be particularly enhanced.

The first element is only required to be one element selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta as described above, but is preferably an element belonging to group 3A or group 4A in the long periodic table among the group consisting of the above-described seven elements. An element belonging to group 3A or group 4A removes oxygen contained as an oxide in the metal powder and therefore can particularly enhance the sinterability of the metal powder. According to this, the concentration of oxygen remaining in the crystal grains after sintering can be decreased. As a result, the content of oxygen in the sintered body can be decreased, and the density can be increased. Further, these elements are elements having high activity, and therefore, are considered to cause rapid atomic diffusion. Accordingly, this atomic diffusion acts as a driving force, and thereby a distance between particles of the metal powder is efficiently decreased and a neck is formed between the particles, so that the densification of a molded body is promoted. As a result, the density of the sintered body can be further increased.

On the other hand, the second element is only required to be one element selected from the group consisting of the following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta and different from the first element as described above, but is preferably an element belonging to group 5A in the long periodic table among the group consisting of the above-described seven elements. An element belonging to group 5A particularly efficiently deposits the above-described carbide or the like, and therefore, can efficiently inhibit the significant growth of crystal grains during sintering. As a result, the production of fine crystal grains is promoted, and thus, the density of the sintered body can be increased and also the mechanical properties of the sintered body can be enhanced.

Incidentally, by the combination of the first element with the second element composed of the elements as described above, the effects of the respective elements are exhibited without inhibiting each other. Due to this, the metal powder containing such a first element and a second element can produce a sintered body having a particularly high density.

More preferably, a combination of an element belonging to group 4A as the first element with Nb as the second element is adopted.

Further more preferably, a combination of Zr or Hf as the first element with Nb as the second element is adopted.

By adopting such a combination, the above-described effect becomes more prominent.

In the case where the first element is particularly Zr, since Zr is a ferrite forming element, a body-centered cubic lattice phase is deposited. This body-centered cubic lattice phase has more excellent sinterability than the other crystal lattice phases, and therefore contributes to the densification of a sintered body.

The atomic radius of Zr is slightly larger than that of Fe. Specifically, the atomic radius of Fe is about 0.117 nm, and the atomic radius of Zr is about 0.145 nm. Therefore, Zr is solid-dissolved in Fe, but is not completely solid-dissolved therein, and part of Zr is deposited as a carbide or the like. Due to this, an appropriate amount of a carbide or the like is deposited, and thus, an increase in the size of crystal grains can be effectively prevented while achieving both promotion of sintering and densification.

In the case where the second element is particularly Nb, the atomic radius of Nb is slightly larger than that of Fe, but slightly smaller than that of Zr. Specifically, the atomic radius of Fe is about 0.117 nm, and the atomic radius of Nb is about 0.134 nm. Therefore, Nb is solid-dissolved in Fe, but is not completely solid-dissolved therein, and part of Nb is deposited as a carbide or the like. Due to this, an appropriate amount of a carbide or the like is deposited, and thus, an increase in the size of crystal grains can be effectively prevented while achieving both promotion of sintering and densification.

The content of the first element in the metal powder is set to 0.01% by mass or more and 0.5% by mass or less, but is set to preferably 0.03% by mass or more and 0.3% by mass or less, more preferably 0.05% by mass or more and 0.2% by mass or less. If the content of the first element is less than the above lower limit, the effect of the addition of the first element is weakened depending on the overall composition so that the density of a sintered body to be produced is not sufficiently increased. On the other hand, if the content of the first element exceeds the above upper limit, the amount of the first element is too much depending on the overall composition so that the ratio of the above-described carbide or the like is too much, and therefore, the densification is impeded instead.

The content of the second element in the metal powder is set to 0.01% by mass or more and 0.5% by mass or less, but is set to preferably 0.03% by mass or more and 0.3% by mass or less, more preferably 0.05% by mass or more and 0.2% by mass or less. If the content of the second element is less than the above lower limit, the effect of the addition of the second element is weakened depending on the overall composition so that the density of a sintered body to be produced is not sufficiently increased. On the other hand, if the content of the second element exceeds the above upper limit, the amount of the second element is too much depending on the overall composition so that the ratio of the above-described carbide or the like is too much, and therefore, the densification is impeded instead.

Further, as described above, each of the first element and the second element deposits a carbide or the like, however, in the case where an element belonging to group 3A or group 4A is selected as the first element as described above and an element belonging to group 5A is selected as the second element as described above, it is presumed that when the metal powder is sintered, the timing when a carbide or the like of the first element is deposited and the timing when a carbide or the like of the second element is deposited differ in moderation. It is considered that due to the difference in timing when a carbide or the like is deposited in this manner, sintering gradually proceeds so that the generation of pores is prevented, and thus, a dense sintered body can be obtained. That is, it is considered that by the existence of both of the carbide or the like of the first element and the carbide or the like of the second element, the increase in the size of crystal grains can be inhibited while increasing the density of the sintered body.

Due to such a difference in timing, the carbide or the like of the first element and the carbide or the like of the second element deposited in the particle 1 are mutually exclusively present. That is, the carbide or the like of the first element and the carbide or the like of the second element are less likely to be deposited at the same site, and are deposited apart from each other in most cases. Then, by the existence of both of the carbide or the like of the first element and the carbide or the like of the second element in this manner, when the particles 1 are sintered, the increase in the size of crystal grains is more reliably prevented, and thus, the density of the sintered body can be increased.

Further, since the carbide or the like of the first element and the carbide or the like of the second element are deposited apart from each other, an effect of preventing the increase in the size of crystal grains is uniformly exhibited in the particle 1. From this viewpoint, the densification of the sintered body is particularly promoted.

In addition, it is considered that in the particle 1, the carbide or the like of the first element and the carbide or the like of the second element act as “nuclei”, and the accumulation of silicon oxide occurs. By the accumulation of silicon oxide at a crystal grain boundary, the concentration of oxides inside the crystal is decreased, and therefore, sintering is promoted. As a result, it is considered that the densification of the sintered body is further promoted when the particles 1 are sintered.

As a result, in the particle 1, the first region P1 which is a region containing Fe as a principal component, the second region P2 in which silicon oxide is accumulated by using the carbide or the like of the first element as a nucleus, and the third region P3 in which silicon oxide is accumulated by using the carbide or the like of the second element as a nucleus are formed.

When such particles 1 are subjected to powder metallurgy, a sintered body can be densified, and therefore, a sintered body having a high density can be produced without performing an additional treatment. It is considered that when the particles 1 are subjected to powder metallurgy, the second region P2 and the third region P3 move to a metal crystal grain boundary in a sintered body. Then, the second region P2 and the third region P3 having moved to the triple point of a crystal grain boundary prevent the crystal growth at this point (a flux pinning effect). As a result, the significant growth of crystal grains is prevented, and thus, a sintered body having finer crystals can be obtained. Such a sintered body has particularly high mechanical properties.

The metal powder is only required to contain two elements selected from the group consisting of the above-described seven elements, but may further contain an element which is selected from this group and is different from these two elements. That is, the metal powder may contain three or more elements selected from the group consisting of the above-described seven elements. According to this, the above-described effect can be further enhanced, which slightly varies depending on the combination of the elements to be contained.

Further, it is preferred to set the ratio of the content of the first element to the content of the second element in consideration of the mass number of each of the first element and the second element.

Specifically, when the value obtained by dividing the content E1 (mass %) of the first element by the mass number of the first element is represented by X1 and the value obtained by dividing the content E2 (mass %) of the second element by the mass number of the second element is represented by X2, X1/X2 is preferably 0.3 or more and 3 or less, more preferably 0.5 or more and 2 or less, further more preferably 0.75 or more and 1.3 or less. By setting the value of X1/X2 within the above range, the balance between the deposition amount of the carbide or the like of the first element and the deposition amount of the carbide or the like of the second element can be optimized. By doing this, pores remaining in a molded body can be eliminated as if they were swept out sequentially from the inside, and therefore, pores generated in a sintered body can be minimized. Accordingly, a metal powder capable of producing a sintered body having a high density and excellent mechanical properties can be obtained by setting the value of X1/X2 within the above range.

Here, with respect a specific example of the combination of the first element with the second element, based on the above-described range of the value of X1/X2, the ratio (E1/E2) of the content E1 of the first element to the content E2 of the second element is calculated.

For example, in the case where the first element is Zr and the second element is Nb, since the mass number of Zr is 91.2 and the mass number of Nb is 92.9, E1/E2 is preferably 0.29 or more and 2.95 or less, more preferably 0.49 or more and 1.96 or less.

In the case where the first element is Hf and the second element is Nb, since the mass number of Hf is 178.5 and the mass number of Nb is 92.9, E1/E2 is preferably 0.58 or more and 5.76 or less, more preferably 0.96 or more and 3.84 or less.

In the case where the first element is Ti and the second element is Nb, since the mass number of Ti is 47.9 and the mass number of Nb is 92.9, E1/E2 is preferably 0.15 or more and 1.55 or less, more preferably 0.26 or more and 1.03 or less.

In the case where the first element is Nb and the second element is Ta, since the mass number of Nb is 92.9 and the mass number of Ta is 180.9, E1/E2 is preferably 0.15 or more and 1.54 or less, more preferably 0.26 or more and 1.03 or less.

In the case where the first element is Y and the second element is Nb, since the mass number of Y is 88.9 and the mass number of Nb is 92.9, E1/E2 is preferably 0.29 or more and 2.87 or less, more preferably 0.48 or more and 1.91 or less.

In the case where the first element is V and the second element is Nb, since the mass number of V is 50.9 and the mass number of Nb is 92.9, E1/E2 is preferably 0.16 or more and 1.64 or less, more preferably 0.27 or more and 1.10 or less.

In the case where the first element is Ti and the second element is Zr, since the mass number of Ti is 47.9 and the mass number of Zr is 91.2, E1/E2 is preferably 0.16 or more and 1.58 or less, more preferably 0.26 or more and 1.05 or less.

In the case where the first element is Zr and the second element is Ta, since the mass number of Zr is 91.2 and the mass number of Ta is 180.9, E1/E2 is preferably 0.15 or more and 1.51 or less, more preferably 0.25 or more and 1.01 or less.

In the case where the first element is Zr and the second element is V, since the mass number of Zr is 91.2 and the mass number of V is 50.9, E1/E2 is preferably 0.54 or more and 5.38 or less, more preferably 0.90 or more and 3.58 or less.

Also in the case of a combination other than the above-described combinations, E1/E2 can be calculated in the same manner as described above.

The presence of the first region P1, the second region P2, and the third region P3 can be determined by, for example, observation using a transmission electron microscope or a mapping analysis by energy dispersive X-ray spectrometry (EDS). FIGS. 3A and 3B show an example of a transmission electron microscope (TEM) image of a cross section of the particle contained in the metal powder for powder metallurgy according to the invention, and FIG. 4 shows an example of the results of a mapping analysis by energy dispersive X-ray spectrometry of the cross section of the particle shown in FIG. 3B.

Among these, FIG. 3A shows an example of a TEM image (a high-angle annular dark-field scanning transmission electron microscope image) of a cross section of the particle 1, and FIG. 3B is a partial enlarged view of this TEM image. In FIG. 3B, the second region P2 or the third region P3 scattered in the first region P1 is indicated by an arrow.

In FIG. 4, “STEM-HAADF” is a partial enlarged view of the TEM image shown in FIG. 3B, “Fe—K” is a mapping image showing the state of distribution of Fe, “Cr—K” is a mapping image showing the state of distribution of Cr, “Ni—K” is a mapping image showing the state of distribution of Ni, “Si—K” is a mapping image showing the state of distribution of Si, “Zr—K” is a mapping image showing the state of distribution of Zr, “Nb—K” is a mapping image showing the state of distribution of Nb, and “O—K” is a mapping image showing the state of distribution of O. Further, an arrow in FIG. 4 indicates the second region P2 or the third region P3. The gray levels appearing in each mapping image show that the content of each element is higher in a region with a lighter gray level, and the content of each element is lower in a region with a darker gray level.

As shown in FIGS. 3A and 3B, it is found that in the particle 1, the second region P2 and the third region P3 are present in a scattered manner in the first region P1, and the second region P2 and the third region P3 are apart from each other.

For example, in the image of “STEM-HAADF” of FIG. 4, five regions in a particle form (regions indicated by arrows) are confirmed, and in each region, the concentration of Si and O and the loss of Fe are confirmed, and therefore, it is found that in these regions, silicon oxide is accumulated. Further, among these five regions, the concentration of Zr (the first element) is confirmed in one region, and the concentration of Nb (the second element) is confirmed in three regions. Therefore, it is considered that the region in which the concentration of Zr is confirmed corresponds to the second region P2, and the region in which the concentration of Nb is confirmed corresponds to the third region P3. It is also considered that the region other than the five regions in a particle form corresponds to the first region P1.

Due to the disposition of the second region P2 and the third region P3 apart from each other in this manner, the structural uniformity of the particle 1 is further enhanced, and therefore, an effect of fining crystal grains in a sintered body can be uniformly exhibited. As a result, a more homogeneous sintered body can be obtained.

The form of each of the second region P2 and the third region P3 may be any form, however, in the case where both regions have a particle form as shown in FIGS. 3A and 3B, the particle diameter of each of the second region P2 and the third region P3 is preferably about 0.01% or more and 0.9% or less, more preferably about 0.05% or more and 0.6% or less, further more preferably 0.1% or more and 0.5% or less of the particle diameter of the particle 1. When the particles 1 including such a second region P2 and a third region P3 are subjected to a firing step, the second region P2 and the third region P3 more easily move to a metal crystal grain boundary in a sintered body, and therefore, the significant growth of crystal grains can be more reliably prevented.

The particle diameter of each of the second region P2 and the third region P3 can be obtained as a diameter of a circle having the same area (circle equivalent diameter) as that of each of the second region P2 and the third region P3 in an enlarged image of the cross section of the particle 1. Further, the particle diameter of the particle 1 can be obtained as a diameter of a circle having the same area (circle equivalent diameter) as that of the projected image of the particle 1. The ratio of the above-described particle diameter can be obtained as an average of the ratio obtained for 10 or more regions of each of the second region P2 and the third region P3.

The “particle form” refers to a state in which the aspect ratio of the shape of the cross section of the second region P2 or the third region P3 is 0.3 or more and 1 or less, and the specific form is not particularly limited, but examples thereof include a circle and a polygon. The aspect ratio refers to a ratio obtained according to the following formula: (a minor axis)/(a major axis) wherein the major axis represents the maximum length of the form of across section, and the minor axis represents the maximum length thereof in the direction perpendicular to the major axis.

The content E1 of the first element and the content E2 of the second element are as described above, respectively, but the sum of the contents of these elements are preferably 0.05% by mass or more and 0.6% by mass or less, more preferably 0.10% by mass or more and 0.48% by mass or less, further more preferably 0.12% by mass or more and 0.24% by mass or less. By setting the sum of the contents of the first element and the second element within the above range, the densification of a sintered body to be produced becomes necessary and sufficient.

When the ratio of the sum of the contents of the first element and the second element to the content of Si is represented by (E1+E2)/Si, (E1+E2)/Si is preferably 0.1 or more and 0.7 or less, more preferably 0.15 or more and 0.6 or less, further more preferably 0.2 or more and 0.5 or less on a mass basis. By setting the value of (E1+E2)/Si within the above range, a decrease in the toughness or the like when Si is added is sufficiently compensated by the addition of the first element and the second element. As a result, a metal powder capable of producing a sintered body which has excellent mechanical properties such as toughness, although the density is high, and also has excellent corrosion resistance attributed to Si can be obtained. In addition, in the case where silicon oxide is accumulated necessarily and sufficiently by using the carbide or the like of the first element or the carbide or the like of the second element as a nucleus in the particle 1, and an element such as Cr or Ni is contained in the particle 1 in addition to Fe, an oxidation reaction of such an element is easily prevented. Therefore, also from this viewpoint, the sinterability of the particle 1 is enhanced, and thus, a sintered body having a higher density, excellent mechanical properties, and excellent corrosion resistance can be obtained.

With respect to the positional relation between the carbide or the like of the first element or the carbide or the like of the second element and silicon oxide, it is not always necessary for the carbide or the like to be a “nucleus” positioned at the center of silicon oxide, and for example, these components may have a positional relation such that silicon oxide is accumulated in the inside of the carbide or the like.

In the particle 1, a region other than the first region P1, the second region P2, and the third region P3 may exist. For example, a region in which the carbide or the like of the first element and the carbide or the like of the second element coexist, a region in which silicon oxide is accumulated in the region, or a region in which only silicon oxide is accumulated may exist.

The first region P1 and the second region P2 in the particle 1 are only required to satisfy all the relations represented by the above-described formulae (1) to (3), but they preferably satisfy all the relations represented by the following formulae (1A) to (3A).

1.5×Zr(P1)<Zr(P2)<10⁵×Zr(P1)  (1A)

1.5×Si(P1)<Si(P2)<10⁵×Si(P1)  (2A)

10⁻⁵×Fe(P1)<Fe(P2)<10⁻¹×Fe(P1)  (3A)

Similarly, the first region P1 and the third region P3 in the particle 1 are only required to satisfy all the relations represented by the above-described formulae (4) to (6), but they preferably satisfy all the relations represented by the following formulae (4A) to (6A).

1.5×Nb(P1)<Nb(P3)<10⁵×Nb(P1)  (4A)

1.5×Si(P1)<Si(P3)<10⁵×Si(P1)  (5A)

10⁻⁵×Fe(P1)<Fe(P3)<10⁻¹×Fe(P1)  (6A)

By allowing the particle 1 to satisfy such relations, the sinterability of the particle 1 is further enhanced, and thus, a sintered body having a higher density, excellent mechanical properties, and excellent corrosion resistance can be obtained.

The relations as described above can be specified by, for example, performing a qualitative and quantitative analysis by energy dispersive X-ray spectrometry (EDS) or wavelength dispersive X-ray spectrometry (WDS) of the respective regions appearing in the cross section of the particle 1.

Further, in the particle 1, it is only necessary that one or more regions of each of the second region P2 and the third region P3 as described above are present in the cross section of the particle 1, and it is preferred that three or more regions of each region is present therein, and it is more preferred that 5 or more and 1000 or less regions of each region is present therein. According to such a particle 1, the effect as described above is sufficiently exhibited without deteriorating the mechanical properties of the sintered body. Incidentally, the “cross section of the particle 1” at this time refers to a cross section selected so that the area of the cross section of the particle 1 becomes 90% or more of the maximum area (the area of the particle 1 in the direction providing the maximum area) of the projected image of the particle 1.

Such particles 1 can be produced by using at least Fe, Si, the first element, and the second element as the starting materials. At this time, by optimizing the proportions of the respective elements, the particles 1 which satisfy the relations as described above can be obtained.

Hereinafter, one example of the composition of an Fe-based alloy forming the particles 1 will be described. This Fe-based alloy contains Fe as a principal component, Cr in a proportion of 10% by mass or more and 30% by mass or less, Si in a proportion of 0.3% by mass or more and 1.2% by mass or less, C in a proportion of 0.005% by mass or more and 1.2% by mass or less, the first element in a proportion of 0.01% by mass or more and 0.5% by mass or less, and the second element in a proportion of 0.01% by mass or more and 0.5% by mass or less.

Here, in the Fe-based alloy, Cr and C are not essential elements and may be omitted, however, by the addition thereof, the effect as described below is brought about.

Cr (chromium) is an element which provides corrosion resistance to a sintered body to be produced. By using the metal powder containing Cr, a sintered body capable of maintaining high mechanical properties over a long period of time can be obtained.

The content of Cr in the Fe-based alloy is set to 10% by mass or more and 30% by mass or less, but is set to preferably 10.5% by mass or more and 21% by mass or less, more preferably 11% by mass or more and 20% by mass or less. If the content of Cr is less than the above lower limit, the corrosion resistance of a sintered body to be produced may be insufficient depending on the overall composition. On the other hand, if the content of Cr exceeds the above upper limit, the sinterability is deteriorated depending on the overall composition so that it may become difficult to increase the density of the sintered body.

In the case where Ni and Mo are contained in the Fe-based alloy, the content of Cr may be appropriately changed according to the contents of Ni and Mo.

For example, when the content of Ni is 7% by mass or more and 22% by mass or less, and the content of Mo is less than 1.2% by mass, the content of Cr is more preferably 18% by mass or more and 20% by mass or less. On the other hand, when the content of Ni is 10% by mass or more and 22% by mass or less, and the content of Mo is 1.2% by mass or more and 5% by mass or less, the content of Cr is more preferably 16% by mass or more and less than 18% by mass.

Further, when the content of Ni is 0.05% by mass or more and 0.6% by mass or less, the content of Cr is more preferably 10% by mass or more and 18% by mass or less.

C (carbon) forms the carbide or the like of the first element and the carbide or the like of the second element as described above by using C in combination with the first element and the second element. Accordingly, as described above, a sintered body having a high density can be obtained.

The content of C in the Fe-based alloy is set to 0.005% by mass or more and 1.2% by mass or less. If the content of C is less than the above lower limit, it becomes difficult to form a sufficient amount of the carbide or the like of the first element or the carbide or the like of the second element depending on the overall composition, and therefore, the density of the sintered body may not be sufficiently increased. On the other hand, if the content of C exceeds the above upper limit, the amount of C is too much with respect to the amount of the first element or the second element depending on the overall composition so that the sinterability of the particle 1 may be deteriorated instead.

In the case where Ni is contained in the Fe-based alloy, the content of C may be appropriately changed according to the content of Ni.

For example, when the content of Ni is 7% by mass or more and 22% by mass or less, the content of C is more preferably 0.005% by mass or more and 0.3% by mass or less.

Further, when the content of Ni is 0.05% by mass or more and 0.6% by mass or less, the content of C is more preferably 0.15% by mass or more and 1.2% by mass or less.

When the ratio of the sum of the contents of the first element and the second element to the content of C is represented by (E1+E2)/C, (E1+E2)/C is preferably 1 or more and 16 or less, more preferably 2 or more and 13 or less, further more preferably 3 or more and 10 or less. By setting the value of (E1+E2)/C within the above range, an increase in the hardness and prevention of a decrease in the toughness brought about by the addition of C, and an increase in the density brought about by the addition of the first element and the second element can be achieved. As a result, the particles 1 capable of producing a sintered body which has excellent mechanical properties such as tensile strength and toughness can be obtained.

In the case where Ni is contained in the Fe-based alloy, the content of Ni is preferably set to 0.05% by mass or more and 22% by mass or less. By adding Ni to the Fe-based alloy, the corrosion resistance and heat resistance of a sintered body to be produced can be further enhanced.

If the content of Ni is less than the above lower limit, the corrosion resistance and the heat resistance of a sintered body to be produced may not be sufficiently enhanced depending on the overall composition. On the other hand, if the content of Ni exceeds the above upper limit, the corrosion resistance and the heat resistance may be deteriorated instead depending on the overall composition.

Other Elements

The Fe-based alloy may contain, other than the above-described elements, at least one element selected from Mn, Mo, Cu, N, and S according to need. These elements may be inevitably contained in some cases.

Mn is an element which provides corrosion resistance and high mechanical properties to a sintered body to be produced.

The content of Mn in the Fe-based alloy is not particularly limited, but is preferably 0.01% by mass or more and 3% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less. By setting the content of Mn within the above range, a sintered body having a higher density and excellent mechanical properties can be obtained.

If the content of Mn is less than the above lower limit, the corrosion resistance and the mechanical properties of a sintered body to be produced may not be sufficiently enhanced depending on the overall composition. On the other hand, if the content of Mn exceeds the above upper limit, the corrosion resistance and the mechanical properties may be deteriorated instead depending on the overall composition.

Mo is an element which enhances the corrosion resistance of a sintered body to be produced.

The content of Mo in the Fe-based alloy is not particularly limited, but is preferably 1% by mass or more and 5% by mass or less, more preferably 1.2% by mass or more and 4% by mass or less, further more preferably 2% by mass or more and 3% by mass or less. By setting the content of Mo within the above range, the corrosion resistance of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body.

Cu is an element which enhances the corrosion resistance of a sintered body to be produced.

The content of Cu in the Fe-based alloy is not particularly limited, but is preferably 5% by mass or less, more preferably 1% by mass or more and 4% by mass or less. By setting the content of Cu within the above range, the corrosion resistance of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body.

When the content of Ni is 0.05% by mass or more and 0.6% by mass or less, the content of Cu is preferably less than 1% by mass, more preferably less than 0.1% by mass. Further, in this case, it is more preferred that the Fe-based alloy substantially contains no Cu (the content of Cu is set to less than 0.01% by mass) excluding the amount of Cu which is inevitably contained. The detailed reasons therefor have not been known, however, this is due to the fear that by the incorporation of Cu, the effect brought about by the first element and the second element as described above may be weakened.

N is an element which enhances the mechanical properties such as proof stress of a sintered body to be produced.

The content of N in the Fe-based alloy is not particularly limited, but is preferably 0.03% by mass or more and 1% by mass or less, more preferably 0.08% by mass or more and 0.3% by mass or less, further more preferably 0.1% by mass or more and 0.25% by mass or less. By setting the content of N within the above range, the mechanical properties such as proof stress of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body.

In order to produce the particles 1 to which N is added, for example, a method using a nitrided starting material, a method of introducing nitrogen gas into a molten metal, a method of performing a nitriding treatment of a produced metal powder, or the like is used.

S is an element which enhances the machinability of a sintered body to be produced.

The content of S in the Fe-based alloy is not particularly limited, but is preferably 0.5% by mass or less, more preferably 0.01% by mass or more and 0.3% by mass or less. By setting the content of S within the above range, the machinability of a sintered body to be produced can be further enhanced without causing a large decrease in the density of the sintered body. Accordingly, the obtained sintered body can be cut out into a desired shape by performing a machining process.

To the Fe-based alloy, W, Co, B, Se, Te, Pd, Al, or the like may be added other than the above-described elements. At this time, the contents of these elements are not particularly limited, but the content of each element is preferably less than 0.1% by mass, and also the total content of these elements is preferably less than 0.2% by mass. These elements may be inevitably contained in some cases.

The Fe-based alloy may contain impurities. Examples of the impurities include all elements other than the above-described elements, and specific examples thereof include Li, Be, Na, Mg, P, K, Ca, Sc, Zn, Ga, Ge, Ag, In, Sn, Sb, Os, Ir, Pt, Au, and Bi. The incorporation amount of these impurity elements is preferably set such that the content of each of the impurity elements is less than the content of each of the above-described constituent elements of the Fe-based alloy. Further, the incorporation amount of these impurity elements is preferably set such that the content of each of the impurity elements is less than 0.03% by mass, more preferably less than 0.02% by mass. Further, the total content of these impurity elements is set to preferably less than 0.3% by mass, more preferably less than 0.2% by mass. These elements do not inhibit the effect as described above as long as the content thereof is within the above range, and therefore may be intentionally added to the Fe-based alloy.

Meanwhile, O (oxygen) may also be intentionally added to or inevitably mixed in the Fe-based alloy, however, the amount thereof is preferably about 0.8% by mass or less, more preferably about 0.5% by mass or less. By controlling the amount of oxygen in the metal powder within the above range, the sinterability is enhanced, and thus, a sintered body having a high density and excellent mechanical properties can be obtained. Incidentally, the lower limit thereof is not particularly set, but is preferably 0.03% by mass or more from the viewpoint of easy mass production or the like.

Further O which is inevitably mixed in the Fe-based alloy in this manner may exist in any state (as any compound) in the particle 1, but exists in the particle 1 as, for example, an oxide of the first element or the second element, or an oxide of Si (silicon oxide).

Therefore, it is preferred that the content of O in each of the second region P2 and the third region P3 is higher than in the first region P1. In such a particle 1, Fe, Cr, or the like is easily reduced, and thus, the amount of oxygen contained inside the crystal becomes relatively smaller. Further, the second region P2 and the third region P3 move to a metal crystal grain boundary in the sintered body so that the significant growth of crystal grains is prevented. As a result, the sinterability of the particle 1 is further enhanced, and thus, a sintered body having a higher density can be obtained.

In other words, when the content of O in the first region P1 is represented by O (P1), the content of O in the second region P2 is represented by O (P2), and the content of O in the third region P3 is represented by O (P3), the particle 1 satisfies all the relations represented by the following formulae (7) and (8).

O(P2)>O(P1)  (7)

O(P3)>O(P1)  (8)

Further, the particle 1 preferably satisfies all the relations represented by the following formulae (7A) and (8A).

1.5×O(P1)<O(P2)<10⁵×O(P1)  (7A)

1.5×O(P1)<O(P3)<10⁵×O(P1)  (8A)

The particle 1 which satisfies such relations is configured such that the first element, the second element, and Si are sufficiently oxidized in the second region P2 and the third region P3, but the content of O in the first region P1 is sufficiently low. Therefore, the sinterability of the particle 1 can be further enhanced while preventing the significant growth of crystal grains, and thus, a sintered body having a higher density can be obtained.

The compositional ratio of the Fe-based alloy can be determined by, for example, Iron and steel—Atomic absorption spectrometric method specified in JIS G 1257 (2000), Iron and steel—ICP atomic emission spectrometric method specified in JIS G 1258 (2007), Iron and steel—Method for spark discharge atomic emission spectrometric analysis specified in JIS G 1253 (2002), Iron and steel—Method for X-ray fluorescence spectrometric analysis specified in JIS G 1256 (1997), gravimetric, titrimetric, and absorption spectrometric methods specified in JIS G 1211 to G 1237, or the like. Specifically, for example, an optical emission spectrometer for solids (spark optical emission spectrometer, model: SPECTROLAB, type: LAVMB08A) manufactured by SPECTRO Analytical Instruments GmbH or an ICP device (model: CIROS-120) manufactured by Rigaku Corporation can be used.

Incidentally, the methods specified in JIS G 1211 to G 1237 are as follows.

JIS G 1211 (2011): Iron and steel—Methods for determination of carbon content

JIS G 1212 (1997): Iron and steel—Methods for determination of silicon content

JIS G 1213 (2001): Iron and steel—Methods for determination of manganese content

JIS G 1214 (1998): Iron and steel—Methods for determination of phosphorus content

JIS G 1215 (2010): Iron and steel—Methods for determination of sulfur content

JIS G 1216 (1997): Iron and steel—Methods for determination of nickel content

JIS G 1217 (2005): Iron and steel—Methods for determination of chromium content

JIS G 1218 (1999): Iron and steel—Methods for determination of molybdenum content

JIS G 1219 (1997): Iron and steel—Methods for determination of copper content

JIS G 1220 (1994): Iron and steel—Methods for determination of tungsten content

JIS G 1221 (1998): Iron and steel—Methods for determination of vanadium content

JIS G 1222 (1999): Iron and steel—Methods for determination of cobalt content

JIS G 1223 (1997): Iron and steel—Methods for determination of titanium content

JIS G 1224 (2001): Iron and steel—Methods for determination of aluminum content

JIS G 1225 (2006): Iron and steel—Methods for determination of arsenic content

JIS G 1226 (1994): Iron and steel—Methods for determination of tin content

JIS G 1227 (1999): Iron and steel—Methods for determination of boron content

JIS G 1228 (2006): Iron and steel—Methods for determination of nitrogen content

JIS G 1229 (1994): Steel—Methods for determination of lead content

JIS G 1232 (1980): Methods for determination of zirconium in steel

JIS G 1233 (1994): Steel—Method for determination of selenium content

JIS G 1234 (1981): Methods for determination of tellurium in steel

JIS G 1235 (1981): Methods for determination of antimony in iron and steel

JIS G 1236 (1992): Method for determination of tantalum in steel

JIS G 1237 (1997): Iron and steel—Methods for determination of niobium content

Further, when C (carbon) and S (sulfur) are determined, particularly, an infrared absorption method after combustion in a current of oxygen (after combustion in a high-frequency induction heating furnace) specified in JIS G 1211 (2011) is also used. Specifically, a carbon-sulfur analyzer, CS-200 manufactured by LECO Corporation can be used.

Further, when N (nitrogen) and O (oxygen) are determined, particularly, a method for determination of nitrogen content in iron and steel specified in JIS G 1228 (2006) and a method for determination of oxygen content in metallic materials specified in JIS Z 2613 (2006) are also used. Specifically, an oxygen-nitrogen analyzer, TC-300/EF-300 manufactured by LECO Corporation can be used.

In the particle 1, the first region P1 is formed from a crystalline material as described above. The first region P1 may be formed from a polycrystal, but is preferably formed from a single crystal. FIGS. 5A and 5B show an example of a TEM image of a cross section of a particle contained in the metal powder for powder metallurgy according to the invention. FIGS. 6A and 6B show an example of a TEM image of a cross section of a particle contained in a metal powder for powder metallurgy in the related art. In FIGS. 5A, 5B, 6A, and 6B, the second region P2 and the third region P3 do not appear, however, the particle shown in FIGS. 5A and 5B is a particle including the second region P2 and the third region P3, and the particle shown in FIGS. 6A and 6B is a particle including no second region P2 or third region P3.

Among these, FIG. 5A is an incident bright-field (BF) image of the cross section of the particle 1, and FIG. 5B is a (1-1-2) reflection excitation dark-field (DF) image of the same field. Further, FIG. 6A is an incident bright-field (BF) image of the cross section of the particle, and FIG. 6B is a (1-10) reflection excitation dark-field (DF) image of the same field. Incidentally, (1-1-2) and (1-10) show Miller indices of electron beam diffraction spots selected when the respective reflection excitation DF images are taken.

In the BF image of the cross section of the particle 1 shown in FIG. 5A, a boundary line corresponding to the crystal grain boundary is not confirmed. Further, the reflection excitation DF image of the cross section of the particle 1 shown in FIG. 5B is an image obtained by selecting a specific diffraction wave, however, the entire particle 1 appears bright. Based on these, it is found that the first region P1 in the particle 1 shown in FIGS. 5A and 5B is formed from a single crystal.

On the other hand, in the BF image of the cross section of the particle shown in FIG. 6A, a boundary line corresponding to the crystal grain boundary is confirmed. Further, in the reflection excitation DF image of the cross section of the particle shown in FIG. 6B, only a part of the particle appears. Based on these, it is found that the particle shown in FIGS. 6A and 6B is formed from a polycrystal.

It is considered that if the first region P1 is formed from a single crystal in this manner, when the particles 1 are subjected to powder metallurgy, the sinterability of the particles 1 is enhanced, and also the second region P2 and the third region P3 more easily move to a metal crystal grain boundary in the sintered body. As a result, the increase in the size of crystals is more reliably prevented, and thus, a sintered body having finer crystals is obtained.

The first region P1 is only required to be formed from a crystalline material as described above, however, the “crystalline material” as used herein refers to a state in which 70% by volume or more of the first region P1 is a single crystal or a polycrystal. In this case, the remainder of the first region P1 other than the single crystal or the polycrystal may be, for example, an amorphous material or a metal glass. Further, whether or not the first region P1 is formed from a crystalline material can be determined by, for example, making an observation of a reflection excitation dark-field image of the cross section of the particle 1 as described above.

It is preferred that the particle 1 in which the first region P1 is formed from a single crystal (the particle 1 in which 70% by volume or more of the first region P1 is a single crystal) as described above is contained in the metal powder for powder metallurgy as much as possible. Specifically, the particle 1 in which the first region P1 is formed from a single crystal is contained in the metal powder for powder metallurgy in an amount of preferably 50% by number or more, more preferably 60% by number or more. According to such a metal powder for powder metallurgy, the effect as described above brought about by the second region P2 and the third region P3 is more reliably exhibited, and thus, a sintered body having fine crystals can be more reliably produced.

The above ratio can be obtained by arbitrarily extracting 20 or more particles in the metal powder for powder metallurgy, obtaining observation images of these particles as shown in FIGS. 5A and 5B, and counting the particles in which a boundary line corresponding to the crystal grain boundary is not present among the extracted particles.

The average particle diameter of the metal powder for powder metallurgy according to the invention is preferably 0.5 μm or more and 30 μm or less, more preferably 1 μm or more and 20 μm or less, further more preferably 2 μm or more and 10 μm or less. By using the metal powder for powder metallurgy having such a particle diameter, pores remaining in a sintered body are extremely reduced, and therefore, a sintered body having a particularly high density and particularly excellent mechanical properties can be produced.

The average particle diameter can be obtained as a particle diameter when the cumulative amount obtained by cumulating the percentages of the particles from the smaller diameter side reaches 50% in a cumulative particle size distribution on a mass basis obtained by laser diffractometry.

If the average particle diameter of the metal powder for powder metallurgy is less than the above lower limit, the moldability is deteriorated in the case where the shape is difficult to mold, and therefore, the sintered density may be decreased. On the other hand, if the average particle diameter of the metal powder exceeds the above upper limit, spaces among the particles become larger during molding, and therefore, the sintered density may be decreased also in this case.

The particle size distribution of the metal powder for powder metallurgy is preferably as narrow as possible. Specifically, when the average particle diameter of the metal powder for powder metallurgy is within the above range, the maximum particle diameter of the metal powder is preferably 200 μm or less, more preferably 150 μm or less. By controlling the maximum particle diameter of the metal powder for powder metallurgy within the above range, the particle size distribution of the metal powder for powder metallurgy can be made narrower, and thus, the density of the sintered body can be further increased.

Here, the “maximum particle diameter” refers to a particle diameter when the cumulative amount obtained by cumulating the percentages of the particles from the smaller diameter side reaches 99.9% in a cumulative particle size distribution on amass basis obtained by laser diffractometry.

When the minor axis of each particle of the metal powder for powder metallurgy is represented by S (μm) and the major axis thereof is represented by L (μm), the average of the aspect ratio defined by S/L is preferably about 0.4 or more and 1 or less, more preferably about 0.7 or more and 1 or less. The metal powder for powder metallurgy having an aspect ratio within this range has a shape relatively close to a spherical shape, and therefore, the packing factor when the metal powder is molded is increased. As a result, the density of the sintered body can be further increased.

Here, the “major axis” is the maximum length in the projected image of the particle, and the “minor axis” is the maximum length in the direction perpendicular to the major axis. Incidentally, the average of the aspect ratio can be obtained as the average of the measured aspect ratios of 100 or more particles.

The tap density of the metal powder for powder metallurgy according to the invention is preferably 3.5 g/cm³ or more, more preferably 4 g/cm³ or more. According to the metal powder for powder metallurgy having such a high tap density, when a molded body is obtained, the interparticle packing efficiency is particularly increased. Therefore, a particularly dense sintered body can be obtained in the end.

The specific surface area of the metal powder for powder metallurgy according to the invention is not particularly limited, but is preferably 0.1 m²/g or more, more preferably 0.2 m²/g or more. According to the metal powder for powder metallurgy having such a large specific surface area, a surface activity (surface energy) is increased so that it is possible to easily sinter the metal powder even if less energy is applied. Therefore, when a molded body is sintered, a difference in sintering rate hardly occurs between the inner side and the outer side of the molded body, and thus, the decrease in the sintered density due to the pores remaining inside the molded body can be prevented.

Method for Producing Sintered Body

Next, a method for producing a sintered body using such a metal powder for powder metallurgy according to the invention will be described.

The method for producing a sintered body includes (A) a composition preparation step in which a composition for producing a sintered body is prepared, (B) a molding step in which a molded body is produced, (C) a degreasing step in which a degreasing treatment is performed, and (D) a firing step in which firing is performed. Hereinafter, the respective steps will be described sequentially.

(A) Composition Preparation Step

First, the metal powder for powder metallurgy according to the invention and a binder are prepared, and these materials are kneaded using a kneader, whereby a kneaded material (composition) is obtained.

In this kneaded material (an embodiment of the compound according to the invention), the metal powder for powder metallurgy is uniformly dispersed.

The metal powder for powder metallurgy according to the invention is produced by, for example, any of a variety of powdering methods such as an atomization method (such as a water atomization method, a gas atomization method, or a spinning water atomization method), a reducing method, a carbonyl method, and a pulverization method.

Among these, the metal powder for powder metallurgy according to the invention is preferably a metal powder produced by an atomization method, and more preferably a metal powder produced by a water atomization method or a spinning water atomization method. The atomization method is a method in which a molten metal (a metal melt) is caused to collide with a fluid (a liquid or a gas) sprayed at a high speed to atomize the metal melt into a fine powder and also to cool the fine powder, whereby a metal powder is produced. By producing the metal powder for powder metallurgy through such an atomization method, an extremely fine powder can be efficiently produced. Further, the shape of the particle of the obtained powder is closer to a spherical shape by the action of surface tension. Due to this, when the metal powder is molded, a molded body having a high packing factor is obtained. That is, a powder capable of producing a sintered body having a high density can be obtained. In addition, the cooling rate of the metal melt is very high, and therefore, the particle 1 in which the second region P2 and the third region P3 are more uniformly distributed can be obtained.

In the case where a water atomization method is used as the atomization method, the pressure of water (hereinafter referred to as “atomization water”) to be sprayed to the molten metal is not particularly limited, but is set to preferably about 75 MPa or more and 120 MPa or less (750 kgf/cm² or more and 1200 kgf/cm² or less), more preferably about 90 MPa or more and 120 MPa or less (900 kgf/cm² or more and 1200 kgf/cm² or less).

The temperature of the atomization water is also not particularly limited, but is preferably set to about 1° C. or higher and 20° C. or lower.

The atomization water is often sprayed in a cone shape such that it has a vertex on the falling path of the metal melt and the outer diameter gradually decreases downward. In this case, the vertex angle θ of the cone formed by the atomization water is preferably about 10° or more and 40° or less, more preferably about 15° or more and 35° or less. According to this, a metal powder for powder metallurgy having a composition as described above can be reliably produced.

Further, by using a water atomization method (particularly, a spinning water atomization method), the metal melt can be particularly quickly cooled. Due to this, a powder having high quality can be obtained over a wide alloy composition range.

The cooling rate when cooling the metal melt in the atomization method is preferably 1×10⁴° C./s or more, more preferably 1×10⁵° C./s or more. By the quick cooling in this manner, a homogeneous metal powder for powder metallurgy can be obtained. As a result, a sintered body having high quality can be obtained. Incidentally, the volume occupancy of the crystalline material as described above in the particle 1 varies depending on the conditions (for example, the alloy composition, the production conditions, etc.) when the metal powder for powder metallurgy is produced. For example, in the case where the cooling rate is increased (for example, in the case of 1×10⁵° C./s or more), the volume of an amorphous material or a metal glass tends to slightly increase, and in the case where the cooling rate is decreased (for example, in the case of 1×10⁴° C./s or more and less than 1×10⁵° C./s), the volume of a crystalline material tends to slightly increase.

The thus obtained metal powder for powder metallurgy may be classified as needed. Examples of the classification method include dry process classification such as sieving classification, inertial classification, and centrifugal classification, and wet process classification such as sedimentation classification.

Examples of the binder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrenic resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, various resins such as polyether, polyvinyl alcohol, polyvinylpyrrolidone, and copolymers thereof, and various organic binders such as various waxes, paraffins, higher fatty acids (such as stearic acid), higher alcohols, higher fatty acid esters, and higher fatty acid amides. These can be used alone or by mixing two or more types thereof.

The content of the binder is preferably about 2% by mass or more and 20% by mass or less, more preferably about 5% by mass or more and 10% by mass or less with respect to the total amount of the kneaded material. By setting the content of the binder within the above range, a molded body can be formed with good moldability, and also the density is increased, whereby the stability of the shape of the molded body and the like can be particularly enhanced. Further, according to this, a difference in size between the molded body and the degreased body, that is, a shrinkage ratio is optimized, whereby a decrease in the dimensional accuracy of the finally obtained sintered body can be prevented. That is, a sintered body having a high density and high dimensional accuracy can be obtained.

In the kneaded material, a plasticizer may be added as needed. Examples of the plasticizer include phthalate esters (such as DOP, DEP, and DBP), adipate esters, trimellitate esters, and sebacate esters. These can be used alone or by mixing two or more types thereof.

Further, in the kneaded material, other than the metal powder for powder metallurgy, the binder, and the plasticizer, for example, any of a variety of additives such as a lubricant, an antioxidant, a degreasing accelerator, and a surfactant can be added as needed.

The kneading conditions vary depending on the respective conditions such as the metal composition or the particle diameter of the metal powder for powder metallurgy to be used, the composition of the binder, and the blending amount thereof. However, for example, the kneading conditions can be set as follows: the kneading temperature: about 50° C. or higher and 200° C. or lower, and the kneading time: about 15 minutes or more and 210 minutes or less.

Further, the kneaded material is formed into a pellet (small particle) as needed. The particle diameter of the pellet is set to, for example, about 1 mm or more and 15 mm or less.

Incidentally, depending on the molding method described below, in place of the kneaded material, a granulated powder may be produced. The kneaded material, the granulated powder, and the like are examples of the composition to be subjected to the molding step described below.

The embodiment of the granulated powder according to the invention is directed to a granulated powder obtained by binding a plurality of metal particles to one another with a binder by subjecting the metal powder for powder metallurgy according to the invention to a granulation treatment.

Examples of the binder to be used for producing the granulated powder include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrenic resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, various resins such as polyether, polyvinyl alcohol, polyvinylpyrrolidone, and copolymers thereof, and various organic binders such as various waxes, paraffins, higher fatty acids (such as stearic acid), higher alcohols, higher fatty acid esters, and higher fatty acid amides. These can be used alone or by mixing two or more types thereof.

Among these, as the binder, a binder containing a polyvinyl alcohol or polyvinylpyrrolidone is preferred. These binder components have a high binding ability, and therefore can efficiently form the granulated powder even in a relatively small amount. Further, the heat decomposability thereof is also high, and therefore, the binder can be reliably decomposed and removed in a short time during degreasing and firing.

The content of the binder is preferably about 0.2% by mass or more and 10% by mass or less, more preferably about 0.3% by mass or more and 5% by mass or less, further more preferably about 0.3% by mass or more and 2% by mass or less with respect to the total amount of the granulated powder. By setting the content of the binder within the above range, the granulated powder can be efficiently formed while preventing significantly large particles from being formed or the metal particles which are not granulated from remaining in a large amount. Further, since the moldability is improved, the stability of the shape of the molded body and the like can be particularly enhanced. Further, by setting the content of the binder within the above range, a difference in size between the molded body and the degreased body, that is, a shrinkage ratio is optimized, whereby a decrease in the dimensional accuracy of the finally obtained sintered body can be prevented.

Further, in the granulated powder, any of a variety of additives such as a plasticizer, a lubricant, an antioxidant, a degreasing accelerator, and a surfactant may be added as needed.

Examples of the granulation treatment include a spray drying method, a tumbling granulation method, a fluidized bed granulation method, and a tumbling fluidized bed granulation method.

In the granulation treatment, a solvent which dissolves the binder is used as needed. Examples of the solvent include inorganic solvents such as water and carbon tetrachloride, and organic solvents such as ketone-based solvents, alcohol-based solvents, ether-based solvents, cellosolve-based solvents, aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, aromatic heterocyclic compound-based solvents, amide-based solvents, halogen compound-based solvents, ester-based solvents, amine-based solvents, nitrile-based solvents, nitro-based solvents, and aldehyde-based solvents, and one type or a mixture of two or more types selected from these solvents is used.

The average particle diameter of the granulated powder is not particularly limited, and is preferably about 10 μm or more and 200 μm or less, more preferably about 20 μm or more and 100 μm or less, further more preferably about 25 μm or more and 60 μm or less. The granulated powder having such a particle diameter has favorable fluidity, and can more faithfully reflect the shape of a molding die.

The average particle diameter can be obtained as a particle diameter when the cumulative amount obtained by cumulating the percentages of the particles from the smaller diameter side reaches 50% in a cumulative particle size distribution on amass basis obtained by laser diffractometry.

(B) Molding Step

Subsequently, the kneaded material or the granulated powder is molded, whereby a molded body having the same shape as that of a desired sintered body is produced.

The method for producing a molded body (molding method) is not particularly limited, and for example, any of a variety of molding methods such as a compact molding (compression molding) method, a metal powder injection molding (MIM: Metal Injection Molding) method, and an extrusion molding method can be used.

The molding conditions in the case of a compact molding method among these methods are preferably such that the molding pressure is about 200 MPa or more and 1000 MPa or less (2 t/cm² or more and 10 t/cm² or less), which vary depending on the respective conditions such as the composition and the particle diameter of the metal powder for powder metallurgy to be used, the composition of the binder, and the blending amount thereof.

The molding conditions in the case of a metal powder injection molding method are preferably such that the material temperature is about 80° C. or higher and 210° C. or lower, and the injection pressure is about 50 MPa or more and 500 MPa or less (0.5 t/cm² or more and 5 t/cm² or less), which vary depending on the respective conditions.

The molding conditions in the case of an extrusion molding method are preferably such that the material temperature is about 80° C. or higher and 210° C. or lower, and the extrusion pressure is about 50 MPa or more and 500 MPa or less (0.5 t/cm² or more and 5 t/cm² or less), which vary depending on the respective conditions.

The thus obtained molded body is in a state where the binder is uniformly distributed in the spaces among the particles of the metal powder.

The shape and size of the molded body to be produced are determined in anticipation of shrinkage of the molded body in the subsequent degreasing step and firing step.

(C) Degreasing Step

Subsequently, the thus obtained molded body is subjected to a degreasing treatment (binder removal treatment), whereby a degreased body is obtained.

Specifically, the binder is decomposed by heating the molded body, whereby the binder is removed from the molded body. In this manner, the degreasing treatment is performed.

Examples of the degreasing treatment include a method of heating the molded body and a method of exposing the molded body to a gas capable of decomposing the binder.

In the case of using the method of heating the molded body, the conditions for heating the molded body are preferably such that the temperature is about 100° C. or higher and 750° C. or lower, and the time is about 0.1 hours or more and 20 hours or less, and more preferably such that the temperature is about 150° C. or higher and 600° C. or lower, and the time is about 0.5 hours or more and 15 hours or less, which slightly vary depending on the composition and the blending amount of the binder. According to this, the degreasing of the molded body can be necessarily and sufficiently performed without sintering the molded body. As a result, it is possible to reliably prevent the binder component from remaining inside the degreased body in a large amount.

The atmosphere when the molded body is heated is not particularly limited, and an atmosphere of a reducing gas such as hydrogen, an atmosphere of an inert gas such as nitrogen or argon, an atmosphere of an oxidative gas such as air, a reduced pressure atmosphere obtained by reducing the pressure of such an atmosphere, or the like can be used.

Examples of the gas capable of decomposing the binder include ozone gas.

Incidentally, by dividing this degreasing step into a plurality of steps in which the degreasing conditions are different, and performing the plurality of steps, the binder in the molded body can be more rapidly decomposed and removed so that the binder does not remain in the molded body.

Further, according to need, the degreased body may be subjected to a machining process such as grinding, polishing, or cutting. The degreased body has a relatively low hardness and relatively high plasticity, and therefore, the machining process can be easily performed while preventing the degreased body from losing its shape. According to such a machining process, a sintered body having high dimensional accuracy can be easily obtained in the end.

(D) Firing Step

The degreased body obtained in the above step (C) is fired in a firing furnace, whereby a sintered body is obtained.

By this firing, in the metal powder for powder metallurgy, diffusion occurs at the boundary surface between the particles, resulting in sintering. At this time, by the mechanism as described above, the degreased body is rapidly sintered. As a result, a sintered body which is entirely dense and has a high density can be obtained.

The firing temperature varies depending on the composition, the particle diameter, and the like of the metal powder for powder metallurgy used in the production of the molded body and the degreased body, but is set to, for example, about 980° C. or higher and 1330° C. or lower, and preferably set to about 1050° C. or higher and 1260° C. or lower.

Further, the firing time is set to 0.2 hours or more and 7 hours or less, but is preferably set to about 1 hour or more and 6 hours or less.

In the firing step, the firing temperature or the below-described firing atmosphere may be changed during the step.

By setting the firing conditions within such a range, it is possible to sufficiently sinter the entire degreased body while preventing the sintering from proceeding excessively to cause oversintering and an increase in the size of the crystal structure. As a result, a sintered body having a high density and particularly excellent mechanical properties can be obtained.

Further, since the firing temperature is a relatively low temperature, it is easy to control the heating temperature in the firing furnace to be constant, and therefore, it is also easy to maintain the temperature of the degreased body constant. As a result, a more homogeneous sintered body can be produced.

Further, since the firing temperature as described above can be sufficiently realized using a common firing furnace, and therefore, an inexpensive firing furnace can be used, and also the running cost can be kept low. In other words, in the case where the temperature exceeds the above-described firing temperature, it is necessary to employ an expensive firing furnace using a special heat resistant material, and also the running cost may be increased.

The atmosphere when performing firing is not particularly limited, however, in consideration of prevention of significant oxidation of the metal powder, an atmosphere of a reducing gas such as hydrogen, an atmosphere of an inert gas such as argon, a reduced pressure atmosphere obtained by reducing the pressure of such an atmosphere, or the like is preferably used.

The thus obtained sintered body has a high density and excellent mechanical properties. That is, a sintered body produced by molding a composition containing the metal powder for powder metallurgy according to the invention and a binder, followed by degreasing and sintering has a higher relative density than a sintered body obtained by sintering a metal powder in the related art. Therefore, according to the invention, a sintered body having a high density which could not be obtained unless an additional treatment such as an HIP treatment is performed can be realized without performing an additional treatment.

Specifically, according to the invention, for example, the relative density can be expected to be increased by 2% or more as compared with the related art, which slightly varies depending on the composition of the metal powder for powder metallurgy.

As a result, the relative density of the obtained sintered body can be expected to be, for example, 97% or more (preferably 98% or more, more preferably 98.5% or more). The sintered body having a relative density within such a range has excellent mechanical properties comparable to those of ingot materials although it has a shape as close as possible to a desired shape by using a powder metallurgy technique, and therefore, the sintered body can be applied to a variety of machine parts, structural parts, and the like with virtually no post-processing.

Further, the tensile strength and the 0.2% proof stress of a sintered body produced by molding a composition containing the metal powder for powder metallurgy according to the invention and a binder, followed by degreasing and sintering are higher than those of a sintered body obtained by performing sintering in the same manner using a metal powder in the related art. It is considered that this is because by optimizing the alloy composition, the sinterability of the metal powder is enhanced, and thus, the mechanical properties of a sintered body to be produced using the metal powder are enhanced.

Further, the sintered body produced as described above has a high surface hardness. Specifically, in the case of, for example, a composition according to austenite-based stainless steel, the Vickers hardness of the surface of the sintered body is expected to be 140 or more and 500 or less, also preferably expected to be 150 or more and 400 or less, which slightly varies depending on the composition of the metal powder for powder metallurgy. In the case of, for example, a composition according to martensite-based stainless steel, the Vickers hardness of the surface of the sintered body is expected to be 570 or more and 1200 or less, also preferably expected to be 600 or more and 1000 or less. The sintered body having such a hardness has particularly high durability.

Incidentally, the sintered body has a sufficiently high density and mechanical properties even without performing an additional treatment, however, in order to further increase the density and enhance the mechanical properties, a variety of additional treatments may be performed.

As the additional treatment, for example, an additional treatment of increasing the density such as the HIP treatment described above may be performed, and also a variety of quenching treatments, a variety of sub-zero treatments, a variety of tempering treatments, and the like may be performed. These additional treatments may be performed alone or two or more treatments thereof may be performed in combination.

In the firing step and the respective additional treatments described above, a light element in the metal powder (in the sintered body) is volatilized, and the composition of the finally obtained sintered body slightly varies from the composition of the metal powder in some cases.

For example, the content of C in the final sintered body may change within the range of 5% or more and 100% or less (preferably within the range of 30% or more and 100% or less) of the content of C in the metal powder for powder metallurgy, which varies depending on the conditions for the step or the treatment.

Also the content of O in the final sintered body may change within the range of 1% or more and 50% or less (preferably within the range of 3% or more and 50% or less) of the content of O in the metal powder for powder metallurgy, which varies depending on the conditions for the step or the treatment.

On the other hand, as described above, the produced sintered body may be subjected to an HIP treatment as part of the additional treatments to be performed as needed, however, even if the HIP treatment is performed, a sufficient effect is not exhibited in many cases. In the HIP treatment, the density of the sintered body can be further increased, however, the density of the sintered body obtained according to the invention has already been sufficiently increased at the end of the firing step in the first place. Therefore, even if the HIP treatment is further performed, densification hardly proceeds any further.

In addition, in the HIP treatment, it is necessary to apply pressure to a material to be treated through a pressure medium, and therefore, the material to be treated may be contaminated, the composition or the physical properties of the material to be treated may unintentionally change accompanying the contamination, or the color of the material to be treated may change accompanying the contamination. Further, by the application of pressure, residual stress is generated or increased in the material to be treated, and a problem such as a change in the shape or a decrease in the dimensional accuracy may occur as the residual stress is released over time.

On the other hand, according to the invention, a sintered body having a sufficiently high density can be produced without performing such an HIP treatment, and therefore, a sintered body having an increased density and also an increased strength can be obtained in the same manner as in the case of performing an HIP treatment. Such a sintered body is less contaminated and discolored, and also an unintended change in the composition or physical properties, or the like occurs less, and also a problem such as a change in the shape or a decrease in the dimensional accuracy occurs less. Therefore, according to the invention, a sintered body having high mechanical strength and dimensional accuracy, and excellent durability can be efficiently produced.

Further, the sintered body produced according to the invention requires almost no additional treatments for enhancing the mechanical properties, and therefore, the composition and the crystal structure tend to become uniform in the entire sintered body. Due to this, the sintered body has high structural anisotropy and therefore has excellent durability against a load from every direction regardless of its shape.

Sintered Body

Next, an embodiment of the sintered body according to the invention will be described.

FIG. 7 is a view schematically showing a cross section of an embodiment of the sintered body according to the invention.

By using the metal powder for powder metallurgy according to the invention as described above, also a sintered body 10 to be obtained has the same characteristics as the metal powder for powder metallurgy as shown in FIG. 7.

That is, the sintered body 10 according to this embodiment includes a first region S1, a second region S2, and a third region S3 as shown in FIG. 7. Among these regions, the first region S1 shown in FIG. 7 occupies a large part of the cross section of the sintered body 10. On the other hand, the second region S2 and the third region S3 shown in FIG. 7 each have a particle form and are scattered apart from each other in the first region S1.

The first region S1, the second region S2, and the third region S3 have the same relation as the first region P1, the second region P2, and the third region P3 in the metal powder for powder metallurgy according to this embodiment.

That is, in the second region S2, the content of the first element is higher than in the first region S1, the content of Si is higher than in the first region S1, and the content of Fe is lower than in the first region S1.

In other words, when the content of the first element in the first region S1 is represented by E1(S1), the content of the first element in the second region S2 is represented by E1(S2), the content of Si in the first region S1 is represented by Si(S1), the content of Si in the second region S2 is represented by Si(S2), the content of Fe in the first region S1 is represented by Fe(S1), and the content of Fe in the second region S2 is represented by Fe(S2), the sintered body 10 satisfies all the relations represented by the following formulae (9) to (11).

E1(S2)>E1(S1)  (9)

Si(S2)>Si(S1)  (10)

Fe(S2)<Fe(S1)  (11)

Further, in the third region S3, the content of the second element is higher than in the first region S1, the content of Si is higher than in the first region S1, and the content of Fe is lower than in the first region S1.

In other words, when the content of the second element in the first region S1 is represented by E2(S1), the content of the second element in the third region S3 is represented by E2(S3), the content of Si in the third region S3 is represented by Si(S3), and the content of Fe in the third region S3 is represented by Fe(S3), the sintered body 10 satisfies all the relations represented by the following formulae (12) to (14).

E2(S3)>E2(S1)  (12)

Si(S3)>Si(S1)  (13)

Fe(S3)<Fe(S1)  (14)

The sintered body 10 including such a first region S1, a second region S2, and a third region S3 has a high density and excellent mechanical properties, and therefore can be widely applied also to, for example, machine parts, structural parts, and the like, to which an external force is applied.

The sintered body 10 according to this embodiment preferably satisfies all the relations represented by the formulae in which the letter “P” in each of the above formulae (1A) to (3A) is replaced with the letter “S”.

Similarly, the sintered body 10 according to this embodiment preferably further satisfies all the relations represented by the formulae in which the letter “P” in each of the above formulae (4A) to (6A) is replaced with the letter “S”.

It is also preferred that the content of O in each of the second region S2 and the third region S3 is higher in the first region S1. In such a sintered body 10, the content of O in the first region S1 is relatively low. It is considered that the first region S1 has a great influence on the mechanical properties of the sintered body 10, and therefore, by decreasing the content of O in the first region S1, a sintered body 10 having excellent mechanical properties can be obtained.

FIGS. 8A and 8B show an example of a transmission electron microscope image of a cross section of the sintered body according to the invention, and FIG. 9 shows an example of the results of a mapping analysis by energy dispersive X-ray spectrometry of the cross section of the sintered body shown in FIG. 8B.

Among these, FIG. 8A shows an example of a TEM image (a bright-field image) of a cross section of the sintered body, and FIG. 8B is a partial enlarged view of this TEM image.

In FIG. 9, “STEM-HAADF” is a high-angle annular dark-field scanning transmission electron microscope image of the same region as shown in FIG. 8B, “Fe—K” is a mapping image showing the state of distribution of Fe, “Cr—K” is a mapping image showing the state of distribution of Cr, “Ni—K” is a mapping image showing the state of distribution of Ni, “Mo—K” is a mapping image showing the state of distribution of Mo, “Si—K” is a mapping image showing the state of distribution of Si, “Zr—K” is a mapping image showing the state of distribution of Zr, “Nb—K” is a mapping image showing the state of distribution of Nb, “Al—K” is a mapping image showing the state of distribution of Al, and “O—K” is a mapping image showing the state of distribution of O. Further, the arrow in FIG. 9 indicates the second region S2. The gray levels appearing in each mapping image show that the content of each element is higher in a region with a lighter gray level, and the content of each element is lower in a region with a darker gray level.

As shown in FIG. 9, in the image of “STEM-HAADF”, one region in a particle form (the region indicated by the arrow) is confirmed, and in this region, the concentration of Si and O and the loss of Fe are confirmed. Based on this, it is found that in this region, silicon oxide is accumulated. Further, in this region, the accumulation of Zr (the first element) is confirmed, and therefore, it is considered that the region corresponds to the second region S2.

Further, as shown in FIG. 9, in the case where the sintered body contains Al, it is preferred that Al is distributed on the outside of Zr. In other words, it is preferred that Al is distributed exclusively with Zr in the vicinity of the second region S2. According to this, for example, even if Al is mixed in the sintered body unintentionally, Al can be retained in the vicinity of the second region S2, so that Al is hardly solid-dissolved in the first region S1, and therefore, the effect of Al on the mechanical properties of the sintered body can be minimized.

Although an observation image is omitted, it is preferred that Al is also distributed in the vicinity of the third region S3 in the same manner.

The form of each of the second region S2 and the third region S3 may be any form, however, in the case where both regions have a particle (circular) form as shown in FIGS. 8A and 8B, the particle diameter of each of the second region S2 and the third region S3 is preferably about 10 nm or more and 1000 nm or less, more preferably about 50 nm or more and 500 nm or less. Such a second region S2 and a third region S3 contribute to the prevention of oxidation of Fe or the like without deteriorating the mechanical properties of the sintered body, respectively, and therefore, a sintered body having particularly excellent mechanical properties can be realized.

The particle diameter of each of the second region S2 and the third region S3 can be obtained as a diameter of a circle having the same area (circle equivalent diameter) as that of each of the second region S2 and the third region S3 in an enlarged image of the cross section of the sintered body.

The second region S2 and the third region S3 may be present at any site in the sintered body, respectively, but are preferably present at a crystal grain boundary. According to this, the effect brought about by the second region S2 and the third region S3 as described above is more prominently exhibited. That is, the effect of decreasing the oxygen concentration inside the crystal is more reliably exhibited, and thus, the mechanical properties of the sintered body can be sufficiently enhanced.

Also in FIG. 8A, it is confirmed that grain boundary lines extend toward the upper left and lower right of the image with the black region (the second region S2) in a particle form observed at the center of the image interposed therebetween, and therefore, it is confirmed that the second region S2 is present at a crystal grain boundary.

It is considered that the second region S2 and the third region S3 in such a sintered body 10 are regions resulting from the translocation of the second region P2 and the third region P3, respectively, in the particle 1 described above. Therefore, when an observation of the sintered body 10 was made and the second region S2 and the third region S3 were confirmed, it is presumed that the second region P2 and the third region P3 were present in the particle 1 used for producing the sintered body 10. The sintered body 10 is a product resulting from the effect as described above of the second region P2 and the third region P3 contained in the particle 1, and therefore is presumed to be a sintered body having a high density and excellent mechanical properties.

Hereinabove, the metal powder for powder metallurgy, the compound, the granulated powder, the sintered body, and the method for producing a sintered body according to the invention are described with reference to preferred embodiments, however, the invention is not limited thereto.

Further, the sintered body according to the invention is used for, for example, parts for transport machinery such as parts for automobiles, parts for bicycles, parts for railcars, parts for ships, parts for airplanes, and parts for space transport machinery (such as rockets); parts for electronic devices such as parts for personal computers and parts for mobile phone terminals; parts for electrical devices such as refrigerators, washing machines, and cooling and heating machines; parts for machines such as machine tools and semiconductor production devices; parts for plants such as atomic power plants, thermal power plants, hydroelectric power plants, oil refinery plants, and chemical complexes; parts for time pieces, metallic tableware, jewels, ornaments such as frames for glasses, and all other sorts of structural parts.

Examples

Next, Examples of the invention will be described.

1. Production of Sintered Body (Zr—Nb Based) Sample No. 1

(1) First, a metal powder having a composition shown in Table 1 produced by a water atomization method was prepared. This metal powder had an average particle diameter of 4.05 μm, a tap density of 4.20 g/cm³, and a specific surface area of 0.23 m²/g.

The composition of the powder shown in Table 1 was identified and determined by an inductively coupled high-frequency plasma optical emission spectrometry (ICP method). In the ICP analysis, an ICP device (model: CIROS-120) manufactured by Rigaku Corporation was used. Further, in the identification and determination of C, a carbon-sulfur analyzer (CS-200) manufactured by LECO Corporation was used. Further, in the identification and determination of O, an oxygen-nitrogen analyzer (TC-300/EF-300) manufactured by LECO Corporation was used.

(2) Subsequently, the metal powder and a mixture (an organic binder) of polypropylene and a wax were weighed at a mass ratio of 9:1 and mixed with each other, whereby a mixed starting material was obtained.

(3) Subsequently, this mixed starting material was kneaded using a kneader, whereby a compound was obtained.

(4) Subsequently, this compound was molded using an injection molding device under the following molding conditions, whereby a molded body was produced.

Molding Conditions

Material temperature: 150° C.

Injection pressure: 11 MPa (110 kgf/cm²)

(5) Subsequently, the obtained molded body was subjected to a heat treatment (degreasing treatment) under the following degreasing conditions, whereby a degreased body was obtained.

Degreasing Conditions

Degreasing temperature: 500° C.

Degreasing time: 1 hour (retention time at the degreasing temperature)

Degreasing atmosphere: nitrogen atmosphere

(6) Subsequently, the obtained degreased body was fired under the following firing conditions, whereby a sintered body was obtained. The shape of the sintered body was determined to be a cylinder with a diameter of 10 mm and a thickness of 5 mm.

Firing Conditions

Firing temperature: 1150° C.

Firing time: 3 hours (retention time at the firing temperature)

Firing atmosphere: argon atmosphere

Sample Nos. 2 to 30

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 1, respectively. The sintered body of the sample No. 30 was obtained by performing an HIP treatment under the following conditions after firing. Further, the sintered bodies of the sample Nos. 18 to 20 were obtained by using the metal powder produced by a gas atomization method, respectively, and indicated as “Gas” in the column of remarks in Table 1.

HIP Treatment Conditions

Heating temperature: 1100° C.

Heating time: 2 hours

Applied pressure: 100 MPa

TABLE 1 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 1 Example 16.43 12.48 0.73 0.018 0.09 0.07 2.11 0.06 0.28 Remainder 1.29 0.16 0.22 8.89 No. 2 Example 17.12 12.63 0.58 0.023 0.07 0.05 2.43 0.12 0.31 Remainder 1.40 0.12 0.21 5.22 No. 3 Example 17.87 13.24 0.65 0.029 0.05 0.09 2.04 0.07 0.42 Remainder 0.56 0.14 0.22 4.83 No. 4 Example 16.19 14.71 0.84 0.011 0.05 0.05 2.89 0.08 0.25 Remainder 1.00 0.10 0.12 9.09 No. 5 Example 17.55 13.88 0.75 0.026 0.09 0.10 2.61 0.11 0.36 Remainder 0.90 0.19 0.25 7.31 No. 6 Example 16.79 11.58 0.52 0.068 0.12 0.03 2.74 0.12 0.22 Remainder 4.00 0.15 0.29 2.21 No. 7 Example 17.49 13.21 0.69 0.054 0.03 0.12 2.15 0.79 0.41 Remainder 0.25 0.15 0.22 2.78 No. 8 Example 16.88 14.15 0.77 0.024 0.24 0.09 2.23 0.28 0.48 Remainder 2.67 0.33 0.43 13.75 No. 9 Example 17.32 12.65 0.48 0.021 0.08 0.26 2.81 0.17 0.29 Remainder 0.31 0.34 0.71 16.19 No. 10 Example 17.25 12.87 0.35 0.065 0.09 0.05 2.15 0.35 0.62 Remainder 1.80 0.14 0.40 2.15 No. 11 Example 17.66 12.55 0.96 0.017 0.07 0.07 2.24 0.05 0.25 Remainder 1.00 0.14 0.15 8.24 No. 12 Example 16.87 12.91 1.12 0.025 0.15 0.19 2.13 0.05 0.25 Remainder 0.79 0.34 0.30 13.60 No. 13 Example 16.78 12.19 0.54 0.019 0.36 0.42 2.25 0.07 0.58 Remainder 0.86 0.78 1.44 41.05 No. 14 Example 16.77 12.89 0.91 0.024 0.14 0.17 2.13 0.05 0.25 Remainder 0.82 0 31 0.34 12.92 No. 15 Example 16.47 12.57 0.87 0.023 0.13 0.15 2.04 0.05 0.25 Remainder 0.87 0.28 0.32 12.17 No. 16 Example 16.75 12.58 0.68 0.007 0.05 0.09 2.84 0.12 0.28 Remainder 0.56 0.14 0.21 20.00 No. 17 Example 17.22 13.54 0.84 0.152 0.08 0.05 2.84 0.12 0.28 Remainder 1.60 0.13 0.15 0.86 No. 18 Example 16.45 12.55 0.72 0.023 0.08 0.08 1.95 0.08 0.07 Remainder 1.00 0.16 0.22 6.96 Gas No. 19 Example 17.26 12.57 0.59 0.032 0.07 0.06 2.64 0.02 0.08 Remainder 1.17 0.13 0.22 4.06 Gas No. 20 Example 17.64 13.41 0.63 0.015 0.04 0.07 2.04 0.06 0.10 Remainder 0.57 0.11 0.17 7.33 Gas No. 21 Comp. Ex. 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 Remainder 0.00 0.07 0.09 2.80 No. 22 Comp. Ex. 17.22 13.32 0.79 0.032 0.05 0.00 2.28 0.09 0.31 Remainder — 0.05 0.06 1.56 No. 23 Comp. Ex. 16.75 14.23 0.75 0.015 0.00 0.00 2.33 0.12 0.33 Remainder — 0.00 0.00 0.00 No. 24 Comp. Ex. 16.43 12.45 0.88 0.021 0.68 0.07 2.58 0.11 0.38 Remainder 9.71 0.75 0.85 35.71 No. 25 Comp. Ex. 16.35 13.04 0.66 0.035 0.06 0.71 2.36 0.05 0.41 Remainder 0.08 0.77 1.17 22.00 No. 26 Comp. Ex. 17.56 13.25 0.15 0.011 0.06 0.07 2.77 0.11 0.27 Remainder 0.86 0.13 0.87 11.82 No. 27 Comp. Ex. 17.56 13.25 1.35 0.055 0.05 0.06 2.86 0.33 0.55 Remainder 0.83 0.11 0.08 2.00 No. 28 Comp. Ex. 17.56 13.25 0.66 0.002 0.01 0.01 2.77 0.11 0.27 Remainder 1.00 0.02 0.03 10.00 No. 29 Comp. Ex. 17.56 13.25 0.35 0.380 0.22 0.07 2.68 0.24 0.45 Remainder 3.14 0.29 0.83 0.76 No. 30 Comp. Ex. 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 Remainder — 0.07 0.09 2.80 HIP treatment

In Table 1, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Sample Nos. 31 to 46

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 2, respectively. The sintered body of the sample No. 46 was obtained by performing an HIP treatment under the following conditions after firing. Further, the sintered bodies of the sample Nos. 39 to 41 were obtained by using the metal powder produced by a gas atomization method, respectively, and indicated as “Gas” in the column of remarks in Table 2.

HIP Treatment Conditions

Heating temperature: 1100° C.

Heating time: 2 hours

Applied pressure: 100 MPa

TABLE 2 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 31 Example 18.94 13.59 0.77 0.048 0.11 0.09 3.48 0.08 0.48 Remainder 1.22 0.20 0.26 4.17 No. 32 Example 18.15 14.75 0.51 0.021 0.08 0.08 3.08 0.95 0.42 Remainder 1.00 0.16 0.31 7.62 No. 33 Example 19.63 11.39 0.32 0.074 0.09 0.05 3.92 0.35 0.62 Remainder 1.80 0.14 0.44 1.89 No. 34 Example 18.67 13.44 0.98 0.065 0.18 0.04 3.32 0.07 0.28 Remainder 4.50 0.22 0.22 3.38 No. 35 Example 18.03 14.87 0.51 0.005 0.04 0.08 3.15 0.02 0.35 Remainder 0.50 0.12 0.24 24.00 No. 36 Example 19.78 12.35 0.42 0.178 0.09 0.08 3.87 0.35 0.62 Remainder 1.13 0.17 0.40 0.96 No. 37 Example 18.65 13.42 0.87 0.061 0.17 0.04 3.29 0.07 0.28 Remainder 4.25 0.21 0.24 3.44 No. 38 Example 18.63 13.46 0.94 0.063 0.16 0.05 3.27 0.07 0.28 Remainder 3.20 0.21 0.22 3.33 No. 39 Example 18.88 13.54 0.87 0.056 0.12 0.11 3.52 0.11 0.12 Remainder 1.09 0.23 0.26 4.11 Gas No. 40 Example 18.21 14.81 0.48 0.025 0.07 0.09 3.11 0.98 0.11 Remainder 0.78 0.16 0.33 6.40 Gas No. 41 Example 19.57 11.44 0.31 0.068 0.08 0.06 4.02 0.51 0.16 Remainder 1.33 0.14 0.45 2.06 Gas No. 42 Comp. Ex. 18.87 11.24 0.57 0.056 0.00 0.07 3.47 0.22 0.29 Remainder 0.00 0.07 0.12 1.25 No. 43 Comp. Ex. 19.56 14.15 0.79 0.032 0.15 0.00 3.75 0.09 0.31 Remainder — 0.15 0.19 4.69 No. 44 Comp. Ex. 18.78 11.42 0.88 0.012 0.58 0.07 2.58 0.11 0.38 Remainder 8.29 0.65 0.74 54.17 No. 45 Comp. Ex. 19.65 14.51 0.66 0.053 0.06 0.89 2.36 0.05 0.41 Remainder 0.07 0.95 1.44 17.92 No. 46 Comp. Ex. 18.87 11.24 0.57 0.056 0.00 0.07 3.47 0.22 0.29 Remainder 0.00 0.07 0.12 1.25 HIP treatment

In Table 2, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Sample Nos. 47 to 64

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 3, respectively. The sintered body of the sample No. 64 was obtained by performing an HIP treatment under the following conditions after firing. Further, the sintered bodies of the sample Nos. 57 to 59 were obtained by using the metal powder produced by a gas atomization method, respectively, and indicated as “Gas” in the column of remarks in Table 3.

HIP Treatment Conditions

Heating temperature: 1100° C.

Heating time: 2 hours

Applied pressure: 100 MPa

TABLE 3 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 47 Example 19.21 8.34 0.62 0.038 0.08 0.06 0.00 0.21 0.48 Remainder 1.33 0.14 0.23 3.68 No. 48 Example 19.74 9.56 0.88 0.041 0.05 0.10 0.08 0.04 0.55 Remainder 0.50 0.15 0.17 3.66 No. 49 Example 18.30 10.12 0.44 0.019 0.15 0.09 0.05 0.07 0.68 Remainder 1.67 0.24 0.55 12.63 No. 50 Example 19.35 8.19 1.05 0.069 0.08 0.06 0.00 0.05 0.18 Remainder 1.33 0.14 0.13 2.03 No. 51 Example 19.45 9.65 0.88 0.007 0.05 0.10 0.08 0.00 0.55 Remainder 0.50 0.15 0.17 21.43 No. 52 Example 18.25 10.25 0.44 0.256 0.15 0.09 0.05 0.07 0.68 Remainder 1.67 0.24 0.55 0.94 No. 53 Example 20.58 21.54 1.15 0.074 0.05 0.09 0.00 1.23 0.75 Remainder 0.56 0.14 0.12 1.89 No. 54 Example 20.34 19.25 1.02 0.068 0.05 0.09 0.00 1.23 0.75 Remainder 0.56 0.14 0.14 2.06 No. 55 Example 16.58 7.45 0.56 0.128 0.06 0.08 0.05 0.48 0.25 Remainder 0.75 0.14 0.25 1.09 No. 56 Example 15.72 10.25 0.36 0.058 0.04 0.09 2.54 0.07 0.21 Remainder 0.44 0.13 0.36 2.24 No. 57 Example 19.11 8.43 0.64 0.045 0.07 0.07 0.00 0.23 0.12 Remainder 1.00 0.14 0.22 3.11 Gas No. 58 Example 19.72 9.65 0.85 0.048 0.06 0.11 0.09 0.05 0.14 Remainder 0.55 0.17 0.20 3.54 Gas No. 59 Example 18.25 10.21 0.46 0.015 0.12 0.12 0.06 0.09 0.18 Remainder 1.00 0.24 0.52 16.00 Gas No. 60 Comp. Ex. 19.11 8.48 0.74 0.064 0.00 0.05 0.00 0.18 0.28 Remainder 0.00 0.05 0.07 0.78 No. 61 Comp. Ex. 18.78 9.77 0.79 0.023 0.08 0.00 0.02 0.09 0.31 Remainder — 0.08 0.10 3.48 No. 62 Comp. Ex. 18.42 8.21 0.39 0.012 0.69 0.07 0.03 0.11 0.38 Remainder 9.86 0.76 1.95 63.33 No. 63 Comp. Ex. 19.21 8.55 0.42 0.021 0.06 0.61 0.02 0.15 0.32 Remainder 0.10 0.67 1.60 31.90 No. 64 Comp. Ex. 19.11 8.48 0.74 0.064 0.00 0.05 0.00 0.18 0.28 Remainder 0.00 0.05 0.07 0.78 HIP treatment

In Table 3, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Sample No. 65

(1) First, a metal powder having a composition shown in Table 4 was produced by a water atomization method in the same manner as in the case of the sample No. 1.

(2) Subsequently, the metal powder was granulated by a spray drying method. The binder used at this time was polyvinyl alcohol, which was used in an amount of 1 part by mass with respect to 100 parts by mass of the metal powder. Further, a solvent (ion exchanged water) was used in an amount of 50 parts by mass with respect to 1 part by mass of polyvinyl alcohol. In this manner, a granulated powder having an average particle diameter of 50 μm was obtained.

(3) Subsequently, this granulated powder was compact-molded under the following molding conditions. In this molding, a press molding machine was used. The shape of the molded body to be produced was determined to be a cube with a side length of 20 mm.

Molding Conditions

Material temperature: 90° C.

Molding pressure: 600 MPa (6 t/cm²)

(4) Subsequently, the obtained molded body was subjected to a heat treatment (degreasing treatment) under the following degreasing conditions, whereby a degreased body was obtained.

Degreasing Conditions

Degreasing temperature: 450° C.

Degreasing time: 2 hours (retention time at the degreasing temperature)

Degreasing atmosphere: nitrogen atmosphere

(5) Subsequently, the obtained degreased body was fired under the following firing conditions, whereby a sintered body was obtained.

Firing Conditions

Firing temperature: 1150° C.

Firing time: 3 hours (retention time at the firing temperature)

Firing atmosphere: argon atmosphere

Sample Nos. 66 to 85

Sintered bodies were obtained in the same manner as in the case of the sample No. 65 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 4, respectively. The sintered body of the sample No. 85 was obtained by performing an HIP treatment under the following conditions after firing.

HIP Treatment Conditions

Heating temperature: 1100° C.

Heating time: 2 hours

Applied pressure: 100 MPa

TABLE 4 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 65 Example 16.43 12.48 0.73 0.018 0.09 0.07 2.11 0.06 0.28 Remainder 1.29 0.16 0.22 8.89 Compact molding No. 66 Example 17.12 12.63 0.58 0.023 0.07 0.05 2.43 0.12 0.31 Remainder 1.40 0.12 0.21 5.22 Compact molding No. 67 Example 17.87 13.24 0.65 0.029 0.05 0.09 2.04 0.07 0.42 Remainder 0.56 0.14 0.22 4.83 Compact molding No. 68 Example 16.19 14.71 0.84 0.011 0.05 0.05 2.89 0.08 0.25 Remainder 1.00 0.10 0.12 9.09 Compact molding No. 69 Example 17.55 13.88 0.75 0.026 0.09 0.10 2.61 0.11 0.36 Remainder 0.90 0.19 0.25 7.31 Compact molding No. 70 Example 16.79 11.58 0.52 0.068 0.12 0.03 2.74 0.12 0.22 Remainder 4.00 0.15 0.29 2.21 Compact molding No. 71 Example 17.49 13.21 0.69 0.054 0.03 0.12 2.15 0.79 0.41 Remainder 0.25 0.15 0.22 2.78 Compact molding No. 72 Example 16.88 14.15 0.77 0.024 0.24 0.09 2.23 0.28 0.48 Remainder 2.67 0.33 0.43 13.75 Compact molding No. 73 Example 17.32 12.65 0.48 0.021 0.08 0.26 2.81 0.17 0.29 Remainder 0.31 0.34 0.71 16.19 Compact molding No. 74 Example 17.25 12.87 0.35 0.065 0.09 0.05 2.15 0.35 0.62 Remainder 1.80 0.14 0.40 2.15 Compact molding No. 75 Example 17.66 12.55 0.96 0.017 0.07 0.07 2.24 0.05 0.25 Remainder 1.00 0.14 0.15 8.24 Compact molding No. 76 Example 16.87 12.91 1.12 0.025 0.15 0.19 2.13 0.05 0.25 Remainder 0.79 0.34 0.30 13.60 Compact molding No. 77 Example 16.78 12.19 0.54 0.019 0.36 0.42 2.25 0.07 0.58 Remainder 0.86 0.78 1.44 41.05 Compact molding No. 78 Example 16.77 12.89 0.91 0.024 0.14 0.17 2.13 0.05 0.25 Remainder 0.82 0.31 0.34 12.92 Compact molding No. 79 Example 16.47 12.57 0.87 0.023 0.13 0.15 2.04 0.05 0.25 Remainder 0.87 0.28 0.32 12.17 Compact molding No. 80 Comp. Ex. 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 Remainder 0.00 0.07 0.09 2.80 Compact molding No. 81 Comp. Ex. 17.22 13.32 0.79 0.032 0.05 0.00 2.28 0.09 0.31 Remainder — 0.05 0.06 1.56 Compact molding No. 82 Comp. Ex. 16.75 14.23 0.75 0.015 0.00 0.00 2.33 0.12 0.33 Remainder — 0.00 0.00 0.00 Compact molding No. 83 Comp. Ex. 16.43 12.45 0.88 0.021 0.68 0.07 2.58 0.11 0.38 Remainder 9.71 0.75 0.85 35.71 Compact molding No. 84 Comp. Ex. 16.35 13.04 0.66 0.035 0.06 0.71 2.36 0.05 0.41 Remainder 0.08 0.77 1.17 22.00 Compact molding No. 85 Comp. Ex. 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 Remainder — 0.07 0.09 2.80 HIP treatment

In Table 4, among the metal powders for powder metallurgy and the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

2. Evaluation of Metal Powder (Zr—Nb Based) 2.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Tables 1 to 4, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Tables 5 to 8.

2.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos., an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Tables 5 to 8. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Tables 5 to 8.

3. Evaluation of Sintered Body (Zr—Nb Based) 3.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos., an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Tables 5 to 8. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

3.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos., the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Tables 5 to 8.

3.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos., the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Tables 5 to 8.

3.4 Evaluation of Tensile Strength

With respect to the sintered bodies of the respective sample Nos., the tensile strength was measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured tensile strength was evaluated according to the following evaluation criteria.

Evaluation Criteria for Tensile Strength (Tables 5 and 8)

A: The tensile strength of the sintered body is 520 MPa or more.

B: The tensile strength of the sintered body is 510 MPa or more and less than 520 MPa.

C: The tensile strength of the sintered body is 500 MPa or more and less than 510 MPa.

D: The tensile strength of the sintered body is 490 MPa or more and less than 500 MPa.

E: The tensile strength of the sintered body is 480 MPa or more and less than 490 MPa.

F: The tensile strength of the sintered body is less than 480 MPa.

Evaluation Criteria for Tensile Strength (Tables 6 and 7)

A: The tensile strength of the sintered body is 560 MPa or more.

B: The tensile strength of the sintered body is 550 MPa or more and less than 560 MPa.

C: The tensile strength of the sintered body is 540 MPa or more and less than 550 MPa.

D: The tensile strength of the sintered body is 530 MPa or more and less than 540 MPa.

E: The tensile strength of the sintered body is 520 MPa or more and less than 530 MPa.

F: The tensile strength of the sintered body is less than 520 MPa.

3.5 Evaluation of 0.2% Proof Stress

With respect to the sintered bodies of the respective sample Nos., the 0.2% proof stress was measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured 0.2% proof stress was evaluated according to the following evaluation criteria.

Evaluation Criteria for 0.2% Proof Stress (Tables 5 and 8)

A: The 0.2% proof stress of the sintered body is 195 MPa or more.

B: The 0.2% proof stress of the sintered body is 190 MPa or more and less than 195 MPa.

C: The 0.2% proof stress of the sintered body is 185 MPa or more and less than 190 MPa.

D: The 0.2% proof stress of the sintered body is 180 MPa or more and less than 185 MPa.

E: The 0.2% proof stress of the sintered body is 175 MPa or more and less than 180 MPa.

F: The 0.2% proof stress of the sintered body is less than 175 MPa.

Evaluation Criteria for 0.2% Proof Stress (Tables 6 and 7)

A: The 0.2% proof stress of the sintered body is 225 MPa or more.

B: The 0.2% proof stress of the sintered body is 220 MPa or more and less than 225 MPa.

C: The 0.2% proof stress of the sintered body is 215 MPa or more and less than 220 MPa.

D: The 0.2% proof stress of the sintered body is 210 MPa or more and less than 215 MPa.

E: The 0.2% proof stress of the sintered body is 205 MPa or more and less than 210 MPa.

F: The 0.2% proof stress of the sintered body is less than 205 MPa.

3.6 Evaluation of Elongation

With respect to the sintered bodies of the respective sample Nos., the elongation was measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured elongation was evaluated according to the following evaluation criteria.

Evaluation Criteria for Elongation (Tables 5 to 8)

A: The elongation of the sintered body is 48% or more.

B: The elongation of the sintered body is 46% or more and less than 48%.

C: The elongation of the sintered body is 44% or more and less than 46%.

D: The elongation of the sintered body is 42% or more and less than 44%.

E: The elongation of the sintered body is 40% or more and less than 42%.

F: The elongation of the sintered body is less than 40%.

The above evaluation results are shown in Tables 5 to 8.

TABLE 5 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 1 Example 4.05 single crystal 15 0.25 24 0.31 Present Present 99.5 165 A A A No. 2 Example 3.79 single crystal 10 0.26 21 0.24 Present Present 99.6 175 A A A No. 3 Example 3.84 single crystal 8 0.28 18 0.22 Present Present 99.3 171 A A A No. 4 Example 3.92 single crystal 7 0.32 13 0.25 Present Present 98.8 153 B A A No. 5 Example 4.56 single crystal 16 0.09 32 0.14 Present Present 99.7 182 A A A No. 6 Example 3.68 single crystal 20 0.41 16 0.38 Present Present 98.7 154 B B A No. 7 Example 3.77 single crystal 8 0.34 28 0.32 Present Present 98.8 156 B B A No. 8 Example 3.81 single crystal 35 0.29 8 0.25 Present Present 98.3 149 B B A No. 9 Example 3.85 single crystal 6 0.32 42 0.29 Present Present 98.1 148 B B B No. 10 Example 4.23 single crystal 15 0.23 24 0.28 Present Present 98.5 152 B B A No. 11 Example 3.21 single crystal 11 0.56 23 0.62 Present Present 98.1 146 B B B No. 12 Example 3.36 single crystal 22 0.51 45 0.53 Present Present 97.8 144 B B C No. 13 Example 6.18 single crystal 15 0.07 12 0.05 Present Present 97.6 142 C C C No. 14 Example 10.8 single crystal 14 0.08 15 0.07 Present Present 97.5 144 B C C No. 15 Example 15.4 single crystal 13 0.07 12 0.08 Present Present 97.2 141 C C C No. 16 Example 5.23 single crystal 8 0.09 18 0.08 Present Present 97.8 141 B B B No. 17 Example 4.42 single crystal 15 0.24 13 0.29 Present Present 97.3 163 B B C No. 18 Example 8.11 single crystal 8 0.51 12 0.61 Present Present 99.3 161 A A A No. 19 Example 7.65 single crystal 5 0.52 10 0.48 Present Present 99.4 171 A A A No. 20 Example 7.25 polycrystal 4 0.56 9 0.44 Present Present 99.1 164 A A A No. 21 Comp. Ex. 3.77 polycrystal 0 — 18 0.32 Absent Present 96.4 128 D D B No. 22 Comp. Ex. 3.94 polycrystal 15 0.32 0 — Present Absent 96.8 134 D D B No. 23 Comp. Ex. 3.65 polycrystal 0 — 0 — Absent Absent 96.2 123 E E C No. 24 Comp. Ex. 4.87 polycrystal 0 — 15 0.15 Absent Present 94.7 115 D D D No. 25 Comp. Ex. 4.25 polycrystal 12 0.23 0 — Present Absent 94.6 118 D D E No. 26 Comp. Ex. 3.64 single crystal 0 — 0 — Absent Absent 94.5 102 E E C No. 27 Comp. Ex. 3.25 single crystal 0 — 0 — Absent Absent 93.5 135 F F E No. 28 Comp. Ex. 4.87 single crystal 0 — 0 — Absent Absent 95.3 118 D D B No. 29 Comp. Ex. 4.66 single crystal 4 0.25 0 — Present Absent 93.2 138 E E F No. 30 Comp. Ex. 3.77 polycrystal 0 — 18 0.32 Absent Present 99.2 175 A A B

TABLE 6 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 31 Example 5.68 single crystal 16 0.08 25 0.11 Present Present 99.3 178 A A A No. 32 Example 4.79 single crystal 11 0.18 20 0.21 Present Present 99.5 185 A A A No. 33 Example 4.05 single crystal 15 0.25 24 0.27 Present Present 98.6 167 B B A No. 34 Example 3.81 single crystal 22 0.29 12 0.31 Present Present 98.8 158 B B A No. 35 Example 3.05 single crystal 7 0.68 17 0.79 Present Present 98.2 162 B B B No. 36 Example 4.25 single crystal 12 0.23 28 0.25 Present Present 97.6 154 B B C No. 37 Example 9.86 single crystal 8 0.51 15 0.66 Present Present 97.8 158 B B B No. 38 Example 14.2 single crystal 14 0.52 24 0.74 Present Present 97.5 154 B C C No. 39 Example 11.53 single crystal 8 0.16 12 0.22 Present Present 99.1 174 A A A No. 40 Example 9.64 single crystal 5 0.36 10 0.42 Present Present 99.2 180 A A A No. 41 Example 8.25 polycrystal 7 0.51 13 0.54 Present Present 98.3 163 B B A No. 42 Comp. Ex. 5.32 Polycrystal 0 — 16 0.11 Absent Present 96.4 127 D D B No. 43 Comp. Ex. 5.48 Polycrystal 20 0.09 0 — Present Absent 96.7 136 D D B No. 44 Comp. Ex. 4.23 Polycrystal 0 — 17 0.24 Absent Present 95.2 121 D D D No. 45 Comp. Ex. 4.51 Polycrystal 10 0.16 0 — Present Absent 94.8 105 E E F No. 46 Comp. Ex. 5.32 polycrystal 0 — 12 0.12 Absent Present 99.2 174 A A B

TABLE 7 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 47 Example 3.97 single crystal 13 0.28 20 0.32 Present Present 99.6 172 A A A No. 48 Example 3.25 single crystal 8 0.56 19 0.58 Present Present 99.3 167 A A B No. 49 Example 6.54 single crystal 20 0.07 16 0.06 Present Present 98.4 142 A A B No. 50 Example 5.48 single crystal 13 0.08 20 0.10 Present Present 98.2 157 B B B No. 51 Example 3.92 single crystal 8 0.28 18 0.30 Present Present 98.4 161 B B B No. 52 Example 3.74 single crystal 20 0.27 15 0.26 Present Present 97.3 148 B B C No. 53 Example 16.45 single crystal 24 0.02 15 0.03 Present Present 97.1 137 C C C No. 54 Example 22.1 single crystal 26 0.03 16 0.04 Present Present 97.0 135 C C C No. 55 Example 10.05 single crystal 8 0.04 16 0.04 Present Present 97.5 138 B B B No. 56 Example 7.23 single crystal 7 0.06 17 0.05 Present Present 98.8 165 B B A No. 57 Example 8.12 single crystal 7 0.56 10 0.64 Present Present 99.3 165 A A A No. 58 Example 7.22 single crystal 4 0.89 9 0.91 Present Present 99.0 160 A A B No. 59 Example 13.65 polycrystal 11 0.06 8 0.12 Present Present 98.2 134 A A B No. 60 Comp. Ex. 3.89 polycrystal 0 — 15 0.31 Absent Present 96.3 127 D D B No. 61 Comp. Ex. 3.47 polycrystal 14 0.25 0 — Present Absent 96.7 136 D D B No. 62 Comp. Ex. 4.25 polycrystal 0 — 16 0.25 Absent Present 94.7 116 D D D No. 63 Comp. Ex. 3.64 polycrystal 16 0.31 0 — Present Absent 95.2 119 D D E No. 64 Comp. Ex. 3.89 polycrystal 0 — 11 0.32 Absent Present 99.4 170 A A B

TABLE 8 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 65 Example 4.05 single crystal 15 0.25 24 0.31 Present Present 99.6 168 A A A No. 66 Example 3.79 single crystal 10 0.26 21 0.24 Present Present 99.6 177 A A A No. 67 Example 3.84 single crystal 8 0.28 18 0.22 Present Present 99.4 172 A A A No. 68 Example 3.92 single crystal 7 0.32 13 0.25 Present Present 98.9 155 B A A No. 69 Example 4.56 single crystal 16 0.09 32 0.14 Present Present 99.7 183 A A A No. 70 Example 3.68 single crystal 20 0.41 16 0.38 Present Present 98.9 158 B B A No. 71 Example 3.77 single crystal 8 0.34 28 0.32 Present Present 99.0 162 B B A No. 72 Example 3.81 single crystal 35 0.29 8 0.25 Present Present 98.5 155 B B A No. 73 Example 3.85 single crystal 6 0.32 42 0.29 Present Present 98.4 156 B B B No. 74 Example 4.23 single crystal 15 0.23 24 0.28 Present Present 98.7 157 B B A No. 75 Example 3.21 single crystal 11 0.56 23 0.62 Present Present 98.4 159 B B B No. 76 Example 3.36 single crystal 22 0.51 45 0.53 Present Present 98.1 150 B B C No. 77 Example 6.18 single crystal 15 0.07 21 0.05 Present Present 97.9 146 C C C No. 78 Example 10.8 single crystal 14 0.08 15 0.07 Present Present 97.8 147 B C C No. 79 Example 15.4 single crystal 13 0.07 12 0.08 Present Present 97.5 144 C C C No. 80 Comp. Ex. 3.77 polycrystal 0 — 18 0.32 Absent Present 96.6 129 D D B No. 81 Comp. Ex. 3.94 polycrystal 15 0.32 0 — Present Absent 96.9 136 D D B No. 82 Comp. Ex. 3.65 polycrystal 0 — 0 — Absent Absent 96.4 128 E E C No. 83 Comp. Ex. 4.87 polycrystal 0 — 15 0.15 Absent Present 94.9 119 D D D No. 84 Comp. Ex. 4.25 polycrystal 12 0.23 0 — Present Absent 94.8 125 D D E No. 85 Comp. Ex. 3.77 polycrystal 0 — 18 0.32 Absent Present 99.3 180 A A B

As apparent from Tables 5 to 8, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example (excluding the sintered body having undergone the HIP treatment). It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example (excluding the sintered body having undergone the HIP treatment).

On the other hand, by comparison of the values of the respective physical properties between the sintered bodies corresponding to Example and the sintered body having undergone the HIP treatment, it was confirmed that the values of the physical properties of the sintered bodies corresponding to Example are all comparable to those of the sintered body having undergone the HIP treatment.

These results revealed that according to the invention, a high density and excellent mechanical properties comparable to those provided by performing the HIP treatment can be provided to the sintered body without performing an additional treatment of increasing the density such as the HIP treatment.

Further, with respect to the sintered bodies having a high density and excellent mechanical properties, it was confirmed that the first region P1 formed from a single crystal, the second region P2 containing Zr (the first element), Si, and O at relatively high concentrations, and the third region P3 containing Nb (the second element), Si, and O at relatively high concentrations are included in the particles of each of the metal powders used for producing the sintered bodies. It was also found that such regions are included in 10 or more particles among 20 particles arbitrarily extracted from each of the metal powders.

In addition, it was confirmed that also in the sintered bodies obtained using such powders, the first region S1 containing Fe as a principal component, the second region S2 containing Zr, Si, and O at relatively high concentrations, and the third region S3 containing Nb, Si, and O at relatively high concentrations are included. These second region S2 and third region S3 each have a particle form, and the particle diameters thereof were from 10 to 1000 nm.

4. Production of Sintered Body (Hf—Nb Based) Sample Nos. 86 to 113

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Tables 9 to 11, respectively.

TABLE 9 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 86 Example 16.25 12.56 0.71 0.02 0.09 0.05 2.09 0.05 0.25 Remainder 1.80 0.14 0.20 8.24 No. 87 Example 17.14 12.54 0.57 0.02 0.07 0.05 2.45 0.09 0.32 Remainder 1.40 0.12 0.21 5.45 No. 88 Example 17.78 13.25 0.53 0.03 0.07 0.08 2.06 0.08 0.41 Remainder 0.88 0.15 0.28 5.56 No. 89 Example 16.25 14.68 0.82 0.01 0.06 0.03 2.89 0.08 0.25 Remainder 2.00 0.09 0.11 7.50 No. 90 Example 17.52 13.87 0.74 0.03 0.09 0.10 2.63 0.11 0.34 Remainder 0.90 0.19 0.26 7.31 No. 91 Example 16.82 12.03 0.53 0.07 0.11 0.04 2.76 0.11 0.23 Remainder 2.75 0.15 0.28 2.17 No. 92 Example 17.52 13.25 0.68 0.06 0.07 0.12 2.21 0.78 0.41 Remainder 0.58 0.19 0.28 3.45 No. 93 Comp. Ex. 16.34 12.84 0.75 0.03 0.00 0.07 2.36 0.11 0.29 Remainder 0.00 0.07 0.09 2.80 No. 94 Comp. Ex. 17.25 13.35 0.82 0.03 0.08 0.00 2.23 0.09 0.32 Remainder — 0.08 0.10 2.86 No. 95 Comp. Ex. 16.75 14.23 0.75 0.02 0.00 0.00 2.33 0.12 0.33 Remainder — 0.00 0.00 0.00 No. 96 Comp. Ex. 16.34 12.54 0.87 0.02 0.71 0.05 2.56 0.11 0.36 Remainder 14.20  0.76 0.87 36.19 No. 97 Comp. Ex. 16.44 13.12 0.65 0.03 0.04 0.68 2.41 0.06 0.42 Remainder 0.06 0.72 1.11 21.18 No. 98 Comp. Ex. 17.63 13.21 0.14 0.01 0.06 0.07 2.77 0.11 0.27 Remainder 0.86 0.13 0.93 10.83 No. 99 Comp. Ex. 17.54 13.33 1.91 0.05 0.07 0.05 2.68 0.34 0.48 Remainder 1.40 0.12 0.06 2.22

TABLE 10 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 100 Example 18.96 13.54 0.82 0.041 0.09 0.05 3.55 0.35 0.41 Remainder 1.80 0.14 0.17 3.41 No. 101 Example 18.25 14.86 0.54 0.021 0.06 0.09 3.12 0.87 0.39 Remainder 0.67 0.15 0.28 7.14 No. 102 Example 19.74 11.32 0.34 0.067 0.09 0.09 3.88 0.45 0.55 Remainder 1.00 0.18 0.53 2.69 No. 103 Comp. Ex. 18.67 11.36 0.78 0.053 0.00 0.07 3.47 0.22 0.29 Remainder 0.00 0.07 0.09 1.32 No. 104 Comp. Ex. 19.54 14.35 0.89 0.022 0.11 0.00 3.75 0.09 0.31 Remainder — 0.11 0.12 5.00 No. 105 Comp. Ex. 18.69 11.87 0.71 0.027 0.54 0.07 3.76 0.12 0.38 Remainder 7.71 0.61 0.86 22.59 No. 106 Comp. Ex. 19.42 14.58 0.62 0.024 0.06 0.66 3.54 0.07 0.41 Remainder 0.09 0.72 1.16 30.00

TABLE 11 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 107 Example 19.21 8.25 0.67 0.035 0.08 0.05 0.00 0.18 0.25 Remainder 1.60 0.13 0.19 3.71 No. 108 Example 19.74 9.62 0.89 0.039 0.06 0.09 0.05 0.08 0.29 Remainder 0.67 0.15 0.17 3.85 No. 109 Example 18.30 10.31 0.43 0.017 0.14 0.09 0.03 0.23 0.41 Remainder 1.56 0.23 0.53 13.53 No. 110 Comp. Ex. 19.11 8.23 0.77 0.055 0.00 0.06 0.00 0.14 0.25 Remainder 0.00 0.06 0.08 1.09 No. 111 Comp. Ex. 18.78 9.45 0.76 0.024 0.07 0.00 0.02 0.11 0.29 Remainder — 0.07 0.09 2.92 No. 112 Comp. Ex. 18.42 8.36 0.38 0.011 0.54 0.08 0.03 0.25 0.28 Remainder 6.75 0.62 1.63 56.36 No. 113 Comp. Ex. 19.21 8.45 0.45 0.018 0.06 0.58 0.04 0.16 0.32 Remainder 0.10 0.64 1.42 35.56

In Tables 9 to 11, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Tables 9 to 11 is omitted.

5. Evaluation of Metal Powder (Hf—Nb Based) 5.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Tables 9 to 11, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Tables 12 to 14.

5.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Tables 9 to 11, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Tables 12 to 14. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Tables 12 to 14.

6. Evaluation of Sintered Body (Hf—Nb Based) 6.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Tables 9 to 11, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Tables 12 to 14. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

6.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Tables 9 to 11, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Tables 12 to 14.

6.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Tables 9 to 11, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Tables 12 to 14.

6.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Tables 9 to 11, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties of the sintered bodies of the respective sample Nos. shown in Table 9 were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8, and the measured values of the physical properties of the sintered bodies of the respective sample Nos. shown in Tables 10 and 11 were evaluated according to the above-described evaluation criteria applied to Tables 6 and 7.

The above evaluation results are shown in Tables 12 to 14.

TABLE 12 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 86 Example 4.12 single crystal 16 0.24 25 0.34 Present Present 99.5 162 A A A No. 87 Example 4.25 single crystal 12 0.29 23 0.24 Present Present 99.3 173 A A A No. 88 Example 4.02 single crystal 7 0.25 19 0.23 Present Present 98.7 160 A A A No. 89 Example 3.88 single crystal 5 0.38 12 0.29 Present Present 98.5 153 B A A No. 90 Example 4.56 single crystal 18 0.08 34 0.13 Present Present 98.9 175 A A A No. 91 Example 3.98 single crystal 22 0.45 17 0.35 Present Present 99.2 170 A A A No. 92 Example 3.77 single crystal 8 0.32 27 0.26 Present Present 98.2 185 B B B No. 93 Comp. Ex. 3.86 polycrystal 0 — 16 0.28 Absent Present 96.4 185 D D B No. 94 Comp. Ex. 3.95 polycrystal 14 0.28 0 — Present Absent 96.8 180 D D B No. 95 Comp. Ex. 4.05 polycrystal 0 — 0 — Absent Absent 96.2 192 E E C No. 96 Comp. Ex. 4.57 polycrystal 0 — 21 0.12 Absent Present 94.7 202 D D D No. 97 Comp. Ex. 4.52 polycrystal 15 0.19 0 — Present Absent 94.6 211 D D E No. 98 Comp. Ex. 3.65 polycrystal 0 — 0 — Absent Absent 94.6 195 E E D No. 99 Comp. Ex. 3.28 polycrystal 0 — 0 — Absent Absent 93.4 214 F F E

TABLE 13 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 100 Example 5.86 single crystal 17 0.26 26 0.33 Present Present 99.1 167 A A A No. 101 Example 4.97 single crystal 12 0.22 19 0.22 Present Present 98.9 170 A A A No. 102 Example 4.25 single crystal 7 0.31 16 0.19 Present Present 98.6 184 B B B No. 103 Comp. Ex. 5.31 polycrystal 0 — 19 0.36 Absent Present 96.3 195 D D B No. 104 Comp. Ex. 5.83 polycrystal 18 0.35 0 — Present Absent 96.6 189 D D B No. 105 Comp. Ex. 4.52 polycrystal 0 — 0 — Absent Absent 95.1 201 D D D No. 106 Comp. Ex. 4.12 polycrystal 0 — 13 0.12 Absent Present 94.9 205 E E F

TABLE 14 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 107 Example 4.08 single crystal 22 0.28 31 0.33 Present Present 99.3 164 A A A No. 108 Example 3.58 single crystal 15 0.31 18 0.26 Present Present 99.0 175 A A A No. 109 Example 6.41 single crystal 7 0.24 14 0.21 Present Present 98.5 182 A A B No. 110 Comp. Ex. 3.98 polycrystal 0 — 19 0.28 Absent Present 96.3 195 D D B No. 111 Comp. Ex. 3.58 polycrystal 19 0.31 0 — Present Absent 96.7 192 D D B No. 112 Comp. Ex. 4.35 polycrystal 0 — 0 — Absent Absent 94.7 205 D D E No. 113 Comp. Ex. 4.56 polycrystal 0 — 16 0.18 Absent Present 95.2 201 D D E

As apparent from Tables 12 to 14, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

7. Production of Sintered Body (Ti—Nb Based) Sample Nos. 114 to 123

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 15, respectively.

Sample No. 124

A metal powder having an average particle diameter of 4.62 μm, a Ti powder having an average particle diameter of 40 μm and a Nb powder having an average particle diameter of 25 μm were mixed, whereby a mixed powder was prepared. In the preparation of the mixed powder, each of the mixing amounts of the metal powder, the Ti powder, and the Nb powder was adjusted so that the composition of the mixed powder was as shown in Table 15.

Then, a sintered body was obtained in the same manner as the method for producing the sintered body of the sample No. 1 using this mixed powder.

TABLE 15 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Ti) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 114 Example 16.52 12.54 0.77 0.015 0.08 0.07 2.13 0.06 0.25 Remainder 1.14 0.15 0.19 10.00 No. 115 Example 16.86 13.15 0.51 0.021 0.08 0.08 2.21 0.51 0.42 Remainder 1.00 0.16 0.31 7.62 No. 116 Example 16.63 11.87 0.81 0.025 0.06 0.10 2.07 0.35 0.24 Remainder 0.60 0.16 0.20 6.40 No. 117 Example 17.12 12.61 0.98 0.065 0.04 0.18 2.23 0.07 0.54 Remainder 0.22 0.22 0.22 3.38 No. 118 Example 16.23 13.54 0.51 0.009 0.04 0.08 2.26 0.02 0.35 Remainder 0.50 0.12 0.24 13.33 No. 119 Example 17.85 12.35 0.42 0.125 0.09 0.08 2.57 0.35 0.25 Remainder 1.13 0.17 0.40 1.36 No. 120 Comp. Ex. 16.87 11.42 0.56 0.056 0.00 0.08 2.47 0.12 0.25 Remainder 0.00 0.08 0.14 1.43 No. 121 Comp. Ex. 17.56 14.51 0.78 0.032 0.12 0.00 2.68 0.11 0.33 Remainder — 0.12 0.15 3.75 No. 122 Comp. Ex. 16.78 11.24 0.87 0.012 0.54 0.06 2.55 0.15 0.32 Remainder 9.00 0.60 0.69 50.00 No. 123 Comp. Ex. 17.65 14.15 0.68 0.053 0.08 0.89 2.63 0.06 0.25 Remainder 0.09 0.97 1.43 18.30 No. 124 Comp. Ex. 16.88 14.10 0.87 0.056 0.45 0.20 2.25 0.08 0.26 Remainder 2.25 0.65 0.75 11.61 Mixed Powder

In Table 15, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 15 is omitted.

8. Evaluation of Metal Powder (Ti—Nb Based) 8.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 15, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 16.

8.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 15, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 16. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 16.

9. Evaluation of Sintered Body (Ti—Nb Based) 9.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 15, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 16. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

9.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 15, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 16.

9.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 15, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 16.

9.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 15, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 16.

TABLE 16 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 114 Example 4.34 single crystal 14 0.31 28 0.37 Present Present 98.9 179 A A A No. 115 Example 4.79 single crystal 9 0.24 26 0.26 Present Present 99.3 178 A A A No. 116 Example 4.05 single crystal 7 0.29 19 0.21 Present Present 99.4 175 A A A No. 117 Example 3.89 single crystal 5 0.36 12 0.28 Present Present 98.7 180 B B A No. 118 Example 4.12 single crystal 18 0.08 28 0.15 Present Present 98.5 185 B B B No. 119 Example 4.26 single crystal 25 0.45 18 0.41 Present Present 98.2 189 B B C No. 120 Comp. Ex. 4.31 polycrystal 0 — 23 0.34 Absent Present 96.5 191 D D B No. 121 Comp. Ex. 4.48 polycrystal 19 0.33 0 — Present Absent 96.6 189 D D B No. 122 Comp. Ex. 4.25 polycrystal 0 — 0 — Absent Absent 95.3 205 D D D No. 123 Comp. Ex. 4.36 polycrystal 0 — 14 0.16 Absent Present 94.7 215 E E F No. 124 Comp. Ex. 4.62 — — — — — Absent Absent 95.9 214 E E F

As apparent from Table 16, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

10. Production of Sintered Body (Nb—Ta Based) Sample Nos. 125 to 134

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 17, respectively.

TABLE 17 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Nb) (Ta) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 125 Example 16.21 12.15 0.63 0.035 0.07 0.12 2.21 0.06 0.38 Remainder 0.58 0.19 0.30 5.43 No. 126 Example 16.74 11.36 0.87 0.042 0.05 0.10 2.26 0.05 0.45 Remainder 0.50 0.15 0.17 3.57 No. 127 Example 16.30 10.25 0.45 0.018 0.12 0.09 2.68 0.08 0.58 Remainder 1.33 0.21 0.47 11.67 No. 128 Example 16.35 13.68 1.03 0.067 0.05 0.08 2.77 0.06 0.22 Remainder 0.63 0.13 0.13 1.94 No. 129 Example 16.45 14.18 0.86 0.009 0.03 0.04 2.45 0.00 0.45 Remainder 0.75 0.07 0.08 7.78 No. 130 Example 16.25 12.35 0.47 0.123 0.15 0.09 2.12 0.08 0.48 Remainder 1.67 0.24 0.51 1.95 No. 131 Comp. Ex. 17.11 12.29 0.74 0.064 0.00 0.05 2.18 0.15 0.29 Remainder 0.00 0.05 0.07 0.78 No. 132 Comp. Ex. 16.78 12.48 0.79 0.023 0.08 0.00 2.06 0.12 0.33 Remainder — 0.08 0.10 3.48 No. 133 Comp. Ex. 16.42 13.65 0.39 0.012 0.69 0.07 2.89 0.08 0.37 Remainder 9.86 0.76 1.95 63.33 No. 134 Comp. Ex. 17.21 10.88 0.42 0.021 0.06 0.61 2.98 0.13 0.35 Remainder 0.10 0.67 1.60 31.90

In Table 17, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 17 is omitted.

11. Evaluation of Metal Powder (Nb—Ta Based) 11.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 17, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 18.

11.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 17, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 18. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 18.

12. Evaluation of Sintered Body (Nb—Ta Based) 12.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 17, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 18. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

12.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 17, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 18.

12.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 17, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 18.

12.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 17, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 18.

TABLE 18 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 125 Example 3.87 single crystal 16 0.26 28 0.36 Present Present 99.0 166 A A A No. 126 Example 4.12 single crystal 12 0.32 24 0.29 Present Present 99.1 167 A A B No. 127 Example 6.45 single crystal 9 0.29 19 0.25 Present Present 98.5 173 A A B No. 128 Example 5.82 single crystal 6 0.38 12 0.29 Present Present 98.3 178 B B B No. 129 Example 3.45 single crystal 18 0.08 34 0.16 Present Present 98.2 175 B B B No. 130 Example 3.25 single crystal 25 0.45 18 0.27 Present Present 97.4 181 B B C No. 131 Comp. Ex. 3.98 polycrystal 0 — 21 0.37 Absent Present 96.3 187 D D B No. 132 Comp. Ex. 3.74 polycrystal 18 0.31 0 — Present Absent 96.0 198 D D B No. 133 Comp. Ex. 4.21 polycrystal 0 — 0 — Absent Absent 93.8 236 D D D No. 134 Comp. Ex. 3.87 polycrystal 0 — 13 0.16 Absent Present 94.2 225 D D E

As apparent from Table 18, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

13. Production of Sintered Body (Y—Nb Based) Sample Nos. 135 to 145

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 19, respectively.

TABLE 19 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Y) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 135 Example 16.55 12.58 0.85 0.025 0.08 0.09 2.13 0.07 0.26 Remainder 0.89 0.17 0.20 6.80 No. 136 Example 17.32 12.87 0.68 0.023 0.05 0.08 2.21 0.11 0.33 Remainder 0.63 0.13 0.19 5.65 No. 137 Example 16.35 12.32 0.74 0.029 0.09 0.05 2.04 0.08 0.41 Remainder 1.80 0.14 0.19 4.83 No. 138 Example 16.31 14.52 0.53 0.011 0.03 0.08 2.68 0.07 0.26 Remainder 0.38 0.11 0.21 10.00 No. 139 Example 17.12 13.88 0.57 0.024 0.09 0.10 2.51 0.12 0.34 Remainder 0.90 0.19 0.33 7.92 No. 140 Example 16.66 11.58 1.02 0.057 0.11 0.04 2.74 0.12 0.22 Remainder 2.75 0.15 0.15 2.63 No. 141 Example 16.21 13.21 0.32 0.044 0.08 0.12 2.15 0.79 0.41 Remainder 0.67 0.20 0.63 4.55 No. 142 Comp. Ex. 16.55 12.74 0.84 0.026 0.00 0.06 2.24 0.13 0.32 Remainder 0.00 0.06 0.07 2.31 No. 143 Comp. Ex. 17.25 12.79 0.74 0.023 0.07 0.00 2.21 0.06 0.27 Remainder — 0.07 0.09 3.04 No. 144 Comp. Ex. 16.87 12.36 0.86 0.029 0.64 0.12 2.64 0.21 0.41 Remainder 5.33 0.76 0.88 26.21 No. 145 Comp. Ex. 16.39 13.11 0.71 0.033 0.08 0.72 2.35 0.06 0.39 Remainder 0.11 0.80 1.13 24.24

In Table 19, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 19 is omitted.

14. Evaluation of Metal Powder (Y—Nb Based) 14.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 19, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 20.

14.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 19, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 20. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 20.

15. Evaluation of Sintered Body (Y—Nb Based) 15.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 20. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

15.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 20.

15.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 20.

15.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 19, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 20.

TABLE 20 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 135 Example 4.11 single crystal 16 0.23 27 0.36 Present Present 99.2 169 A A A No. 136 Example 3.89 single crystal 11 0.31 25 0.28 Present Present 99.1 170 A A B No. 137 Example 3.94 single crystal 9 0.35 19 0.24 Present Present 99.0 172 A A A No. 138 Example 4.23 single crystal 6 0.28 15 0.26 Present Present 98.7 177 B A A No. 139 Example 4.12 single crystal 18 0.11 36 0.15 Present Present 99.2 174 A A A No. 140 Example 3.87 single crystal 26 0.43 18 0.41 Present Present 98.5 180 B B B No. 141 Example 3.69 single crystal 9 0.36 32 0.28 Present Present 98.4 181 B B B No. 142 Comp. Ex. 3.77 polycrystal 0 — 23 0.36 Absent Present 96.1 192 D D B No. 143 Comp. Ex. 3.94 polycrystal 18 0.28 0 — Present Absent 95.9 196 D D B No. 144 Comp. Ex. 4.78 polycrystal 0 — 0 — Absent Absent 94.8 201 D E E No. 145 Comp. Ex. 4.56 polycrystal 0 — 9 0.17 Absent Present 94.6 204 D E E

As apparent from Table 20, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

16. Production of Sintered Body (V—Nb Based) Sample Nos. 146 to 155

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 21, respectively.

TABLE 21 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (V) (Nb) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 146 Example 16.56 12.65 0.79 0.025 0.08 0.15 2.35 0.06 0.26 Remainder 0.53 0.23 0.29 9.20 No. 147 Example 16.42 12.36 0.71 0.016 0.05 0.10 2.28 0.09 0.31 Remainder 0.50 0.15 0.21 9.38 No. 148 Example 17.23 12.15 0.89 0.022 0.15 0.12 2.23 0.07 0.68 Remainder 1.25 0.27 0.30 12.27 No. 149 Example 17.89 11.75 0.97 0.047 0.09 0.09 2.59 0.05 0.18 Remainder 1.00 0.18 0.19 3.83 No. 150 Example 18.23 13.21 0.88 0.011 0.05 0.10 2.87 0.07 0.31 Remainder 0.50 0.15 0.17 13.64 No. 151 Example 18.25 10.25 0.44 0.187 0.12 0.12 2.47 0.07 0.47 Remainder 1.00 0.24 0.55 1.28 No. 152 Comp. Ex. 16.54 12.74 0.58 0.056 0.00 0.06 2.68 0.12 0.28 Remainder 0.00 0.06 0.10 1.07 No. 153 Comp. Ex. 16.39 12.47 0.75 0.032 0.09 0.00 2.13 0.11 0.32 Remainder — 0.09 0.12 2.81 No. 154 Comp. Ex. 17.87 12.48 0.36 0.014 0.68 0.09 2.54 0.18 0.44 Remainder 7.56 0.77 2.14 55.00 No. 155 Comp. Ex. 17.65 12.77 0.47 0.023 0.07 0.63 2.77 0.16 0.39 Remainder 0.11 0.70 1.49 30.43

In Table 21, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 21 is omitted.

17. Evaluation of Metal Powder (V—Nb Based) 17.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 21, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 22.

17.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 21, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 22. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 22.

18. Evaluation of Sintered Body (V—Nb Based) 18.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 22. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

18.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 22.

18.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 22.

18.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 21, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 22.

TABLE 22 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 146 Example 4.12 single crystal 19 0.27 28 0.28 Present Present 98.9 172 A A B No. 147 Example 4.25 single crystal 12 0.25 22 0.34 Present Present 99.0 167 A A A No. 148 Example 6.89 single crystal 9 0.29 16 0.23 Present Present 98.5 175 A A B No. 149 Example 5.74 single crystal 6 0.36 14 0.28 Present Present 98.3 181 B B B No. 150 Example 3.25 single crystal 17 0.11 38 0.21 Present Present 98.7 161 B B A No. 151 Example 4.11 single crystal 25 0.43 17 0.35 Present Present 97.4 194 B B C No. 152 Comp. Ex. 3.98 polycrystal 0 — 22 0.38 Absent Present 96.2 202 D D C No. 153 Comp. Ex. 3.74 polycrystal 16 0.28 0 — Present Absent 96.0 211 D D C No. 154 Comp. Ex. 4.52 polycrystal 0 — 0 — Absent Absent 94.5 215 D D D No. 155 Comp. Ex. 3.45 polycrystal 0 — 16 0.16 Absent Present 94.3 223 D D E

As apparent from Table 22, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

19. Production of Sintered Body (Ti—Zr Based) Sample Nos. 156 to 165

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 23, respectively.

TABLE 23 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Ti) (Zr) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 156 Example 16.85 12.74 0.86 0.023 0.06 0.12 2.54 0.07 0.31 Remainder 0.50 0.18 0.21 7.83 No. 157 Example 17.24 12.14 0.74 0.039 0.05 0.10 2.36 0.04 0.49 Remainder 0.50 0.15 0.20 3.85 No. 158 Example 16.21 12.46 0.62 0.019 0.12 0.09 2.78 0.07 0.54 Remainder 1.33 0.21 0.34 11.05 No. 159 Example 16.57 12.98 0.97 0.059 0.08 0.06 2.23 0.05 0.21 Remainder 1.33 0.14 0.14 2.37 No. 160 Example 17.85 12.41 0.88 0.009 0.05 0.10 2.74 0.07 0.35 Remainder 0.50 0.15 0.17 16.67 No. 161 Example 17.65 13.21 0.44 0.175 0.09 0.09 2.68 0.07 0.44 Remainder 1.00 0.18 0.41 1.03 No. 162 Comp. Ex. 17.44 12.47 0.72 0.055 0.00 0.06 2.75 0.18 0.26 Remainder 0.00 0.06 0.08 1.09 No. 163 Comp. Ex. 16.54 12.87 0.78 0.032 0.09 0.00 2.69 0.08 0.35 Remainder — 0.09 0.12 2.81 No. 164 Comp. Ex. 16.32 13.58 0.38 0.021 0.64 0.08 2.41 0.07 0.28 Remainder 8.00 0.72 1.89 34.29 No. 165 Comp. Ex. 16.25 13.75 0.43 0.018 0.07 0.59 2.21 0.06 0.22 Remainder 0.12 0.66 1.53 36.67

In Table 23, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 23 is omitted.

20. Evaluation of Metal Powder (Ti—Zr Based) 20.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 23, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 24.

20.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 23, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 24. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 24.

21. Evaluation of Sintered Body (Ti—Zr Based) 21.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 24. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

21.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 24.

21.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 24.

21.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 23, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 24.

TABLE 24 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 156 Example 4.12 single crystal 16 0.27 18 0.34 Present Present 98.8 172 A A B No. 157 Example 4.25 single crystal 8 0.21 24 0.24 Present Present 99.0 167 A A A No. 158 Example 5.87 single crystal 5 0.36 26 0.36 Present Present 98.6 184 A A B No. 159 Example 5.12 single crystal 3 0.45 18 0.29 Present Present 98.5 191 B B B No. 160 Example 3.89 single crystal 28 0.11 45 0.21 Present Present 98.2 195 B B B No. 161 Example 4.47 single crystal 16 0.49 29 0.41 Present Present 97.4 199 B B C No. 162 Comp. Ex. 4.11 polycrystal 0 — 25 0.26 Absent Present 96.3 205 D D C No. 163 Comp. Ex. 3.78 polycrystal 17 0.35 0 — Present Absent 96.7 211 D D C No. 164 Comp. Ex. 4.52 polycrystal 0 — 0 — Absent Absent 94.7 235 D D E No. 165 Comp. Ex. 3.88 polycrystal 0 — 12 0.12 Absent Present 95.2 221 D D E

As apparent from Table 24, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

22. Production of Sintered Body (Zr—Ta Based) Sample Nos. 166 to 175

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 25, respectively.

TABLE 25 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Ti) (Zr) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 166 Example 16.61 12.45 0.68 0.023 0.06 0.09 2.55 0.11 0.38 Remainder 0.67 0.15 0.22 6.52 No. 167 Example 16.94 12.21 0.72 0.039 0.05 0.10 2.47 0.06 0.24 Remainder 0.50 0.15 0.21 3.85 No. 168 Example 17.43 12.89 0.85 0.019 0.12 0.09 2.05 0.54 0.49 Remainder 1.33 0.21 0.25 11.05 No. 169 Example 17.21 13.42 0.97 0.058 0.08 0.06 2.78 0.07 0.31 Remainder 1.33 0.14 0.14 2.41 No. 170 Example 16.31 12.87 0.88 0.011 0.05 0.10 2.74 0.12 0.55 Remainder 0.50 0.15 0.17 13.64 No. 171 Example 16.54 12.25 0.44 0.146 0.09 0.09 2.32 0.07 0.68 Remainder 1.00 0.18 0.41 1.23 No. 172 Comp. Ex. 17.24 12.14 0.77 0.018 0.00 0.06 2.56 0.08 0.27 Remainder 0.00 0.06 0.08 3.33 No. 173 Comp. Ex. 16.87 12.56 0.82 0.026 0.09 0.00 2.24 0.09 0.32 Remainder — 0.09 0.11 3.46 No. 174 Comp. Ex. 16.54 12.32 0.35 0.025 0.78 0.05 2.89 0.11 0.35 Remainder 15.60  0.83 2.37 33.20 No. 175 Comp. Ex. 16.35 12.47 0.45 0.022 0.04 0.58 2.77 0.16 0.33 Remainder 0.07 0.62 1.38 28.18

In Table 25, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 25 is omitted.

23. Evaluation of Metal Powder (Zr—Ta Based) 23.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 25, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 26.

23.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 25, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 26. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 26.

24. Evaluation of Sintered Body (Zr—Ta Based) 24.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 26. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

24.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 26.

24.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 26.

24.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 25, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 26.

TABLE 26 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 166 Example 4.12 single crystal 18 0.31 24 0.47 Present Present 99.2 172 A A A No. 167 Example 4.32 single crystal 11 0.25 21 0.24 Present Present 99.3 167 A A A No. 168 Example 5.74 single crystal 9 0.29 18 0.31 Present Present 98.7 181 A A B No. 169 Example 5.21 single crystal 6 0.36 13 0.28 Present Present 98.5 185 B B B No. 170 Example 4.32 single crystal 18 0.11 32 0.16 Present Present 98.2 189 B B B No. 171 Example 4.23 single crystal 25 0.45 16 0.42 Present Present 97.5 197 B B C No. 172 Comp. Ex. 3.88 polycrystal 0 — 18 0.36 Absent Present 96.2 199 D D C No. 173 Comp. Ex. 4.22 polycrystal 16 0.38 0 — Present Absent 96.2 199 D D C No. 174 Comp. Ex. 4.11 polycrystal 0 — 0 — Absent Absent 94.8 211 D D E No. 175 Comp. Ex. 3.89 polycrystal 0 — 15 0.16 Absent Present 95.1 205 D D E

As apparent from Table 26, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example.

25. Production of Sintered Body (Zr—V Based) Sample Nos. 176 to 185

Sintered bodies were obtained in the same manner as the method for producing the sintered body of the sample No. 1 except that the composition and the like of the metal powder for powder metallurgy were changed as shown in Table 27, respectively.

TABLE 27 Metal powder for powder metallurgy Alloy composition E1 + E1 E2 E2 (E1 + (E1 + Sample Cr Ni Si C (Ti) (Zr) Mo Mn O Fe E1/E2 mass E2)/Si E2)/C Remarks No. — mass % — % — — — No. 176 Example 16.58 12.47 0.75 0.022 0.09 0.06 2.36 0.08 0.31 Remainder 1.50 0.15 0.20 6.82 No. 177 Example 16.32 12.24 0.89 0.015 0.05 0.08 2.64 0.06 0.25 Remainder 0.63 0.13 0.15 8.67 No. 178 Example 16.87 12.55 0.98 0.025 0.09 0.09 2.88 0.07 0.39 Remainder 1.00 0.18 0.18 7.20 No. 179 Example 17.28 12.36 0.54 0.069 0.12 0.06 2.12 0.05 0.23 Remainder 2.00 0.18 0.33 2.61 No. 180 Example 17.59 12.98 0.88 0.012 0.08 0.08 2.58 0.02 0.45 Remainder 1.00 0.16 0.18 13.33 No. 181 Example 17.25 12.78 0.44 0.118 0.09 0.09 2.68 0.07 0.61 Remainder 1.00 0.18 0.41 1.53 No. 182 Comp. Ex. 16.34 12.63 0.77 0.054 0.00 0.06 2.84 0.08 0.36 Remainder 0.00 0.06 0.08 1.11 No. 183 Comp. Ex. 16.78 12.24 0.78 0.032 0.09 0.00 2.64 0.11 0.27 Remainder — 0.09 0.12 2.81 No. 184 Comp. Ex. 16.24 12.36 0.38 0.021 0.61 0.08 2.31 0.09 0.18 Remainder 7.63 0.69 1.82 32.86 No. 185 Comp. Ex. 17.12 12.89 0.45 0.025 0.08 0.59 2.15 0.05 0.24 Remainder 0.14 0.67 1.49 26.80

In Table 27, among the sintered bodies of the respective sample Nos., those corresponding to the invention are indicated as “Example”, and those not corresponding to the invention are indicated as “Comp. Ex.” (Comparative Example).

Further, each sintered body contained very small amounts of impurities, but the description thereof in Table 27 is omitted.

26. Evaluation of Metal Powder (Zr—V Based) 26.1 Evaluation of Crystallinity

With respect to the cross sections of 20 particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 27, the crystallinity of the first region P1 was evaluated using a transmission electron microscope.

As a result, in most of the metal powders for powder metallurgy corresponding to Example, the first region P1 was formed from a single crystal in more than half of the examined particles. Further, in each particle of each of the metal powders for powder metallurgy corresponding to Example, the first region P1 occupied 50% by volume or more of the particle.

On the other hand, in some metal powders for powder metallurgy corresponding to Comparative Example, the first region P1 was formed from a polycrystal in more than half of the examined particles.

The above evaluation results are shown in Table 28.

26.2 Evaluation of Second Region P2 and Third Region P3

With respect to the cross sections of particles of each of the metal powders for powder metallurgy of the respective sample Nos. shown in Table 27, an observation of the second region P2 and the third region P3 was made using a transmission electron microscope. Then, with respect to the second region P2 and the third region P3, the number of each region and the ratio of the particle diameter of each region to the particle diameter of the particle were obtained and are shown in Table 28. The number of each of the second region P2 and the third region P3, the particle diameter thereof, and the particle diameter of the particle were determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS). Further, as the ratio of the particle diameter, an average is shown in Table 28.

27. Evaluation of Sintered Body (Zr—V Based) 27.1 Evaluation of Second Region S2 and Third Region S3

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, an observation of the second region S2 and the third region S3 was made using a transmission electron microscope. Then, a case where the second region S2 or the third region S3 was present is indicated as “present”, and a case where the second region S2 or the third region S3 was not confirmed is indicated as “absent” in Table 28. The presence or absence of the second region S2 or the third region S3 was determined based on a mapping analysis by energy dispersive X-ray spectrometry (EDS).

27.2 Evaluation of Relative Density

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, the sintered density was measured in accordance with the method for measuring the density of sintered metal materials specified in JIS Z 2501 (2000), and also the relative density of each sintered body was calculated with reference to the true density of the metal powder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 28.

27.3 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, the Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 28.

27.4 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shown in Table 27, the tensile strength, 0.2% proof stress, and elongation were measured in accordance with the metal material tensile test method specified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluated according to the above-described evaluation criteria applied to Tables 5 and 8.

The above evaluation results are shown in Table 28.

TABLE 28 Metal powder for powder metallurgy Second Third region P2 region P3 Particle Particle Evaluation results of sintered body Average First Num- diam- Num- diam- Second Third 0.2% particle region P1 ber eter ber eter region region Relative Vickers Tensile proof Elonga- Sample diameter Crystallinity Re- ratio Re- ratio S2 S3 density hardness strength stress tion No. — μm — gions % gions % — — % — — — — No. 176 Example 4.15 single crystal 18 0.31 28 0.39 Present Present 99.3 172 A A A No. 177 Example 4.26 single crystal 12 0.27 18 0.28 Present Present 98.9 167 A A B No. 178 Example 5.74 single crystal 9 0.25 16 0.22 Present Present 99.0 180 A A B No. 179 Example 5.12 single crystal 5 0.38 12 0.28 Present Present 99.1 178 B B B No. 180 Example 3.86 single crystal 14 0.11 39 0.16 Present Present 98.3 197 B B B No. 181 Example 3.65 single crystal 28 0.45 15 0.34 Present Present 97.5 202 B B C No. 182 Comp. Ex. 4.05 polycrystal 0 — 17 0.39 Absent Present 96.2 209 D D C No. 183 Comp. Ex. 4.13 polycrystal 12 0.42 0 — Present Absent 96.5 208 D D C No. 184 Comp. Ex. 4.05 polycrystal 0 — 0 — Absent Absent 94.7 225 D D E No. 185 Comp. Ex. 3.88 polycrystal 0 — 14 0.12 Absent Present 95.2 212 D D E

As apparent from Table 28, it was confirmed that the sintered bodies corresponding to Example each have a higher relative density than the sintered bodies corresponding to Comparative Example. It was also confirmed that there is a significant difference in properties such as tensile strength, 0.2% proof stress, and elongation between the sintered bodies corresponding to Example and the sintered bodies corresponding to Comparative Example. 

What is claimed is:
 1. A metal powder for powder metallurgy, wherein when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the metal powder comprises particles each having: a first region containing Fe as a principal component; a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region; and a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and the first region occupies 50% by volume or more of each of the particles and also is crystalline.
 2. The metal powder for powder metallurgy according to claim 1, wherein the content of O in each of the second region and the third region is higher than in the first region.
 3. The metal powder for powder metallurgy according to claim 1, wherein the second region and the third region are present in the first region and are disposed apart from each other.
 4. The metal powder for powder metallurgy according to claim 1, wherein in the cross section of each of the particles, the second region and the third region each have a particle form, and the particle diameter of each of the second region and the third region is 0.01% or more and 0.9% or less of the particle diameter of the particle.
 5. The metal powder for powder metallurgy according to claim 1, wherein in each of the particles, the first region is formed from a single crystal.
 6. The metal powder for powder metallurgy according to claim 5, wherein in the metal powder for powder metallurgy, the particles are contained in an amount of 50% by number or more.
 7. The metal powder for powder metallurgy according to claim 1, wherein each of the particles contains: Fe as a principal component; Cr in a proportion of 10% by mass or more and 30% by mass or less; Si in a proportion of 0.3% by mass or more and 1.2% by mass or less; C in a proportion of 0.005% by mass or more and 1.2% by mass or less; the first element in a proportion of 0.01% by mass or more and 0.5% by mass or less; and the second element in a proportion of 0.01% by mass or more and 0.5% by mass or less.
 8. A compound, comprising the metal powder for powder metallurgy according to claim 1 and a binder which binds the particles of the metal powder for powder metallurgy to one another.
 9. A granulated powder, wherein the granulated powder is obtained by granulating the metal powder for powder metallurgy according to claim
 1. 10. A sintered body, wherein when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the sintered body comprises: a first region containing Fe as a principal component; a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region; and a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region.
 11. The sintered body according to claim 10, wherein the content of O in each of the second region and the third region is higher than in the first region.
 12. The sintered body according to claim 10, wherein in the cross section of the sintered body, the second region and the third region each have a particle form with a particle diameter of 10 nm or more and 1000 nm or less.
 13. A method for producing a sintered body, comprising: molding a composition containing a metal powder for powder metallurgy, thereby obtaining a molded body; and firing the molded body, thereby obtaining a sintered body, wherein when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the metal powder for powder metallurgy includes particles each having a first region containing Fe as a principal component, a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and the first region occupies 50% by volume or more of each of the particles and also is crystalline. 